Flatten tests/rest/client/{v1,v2_alpha} too (#10667)

1 files changed, 1345 insertions, 0 deletions

diff --git a/tests/rest/client/test_login.py b/tests/rest/client/test_login.py
new file mode 100644
index 0000000000..5b2243fe52
--- /dev/null
+++ b/tests/rest/client/test_login.py
@@ -0,0 +1,1345 @@
+# Copyright 2019-2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import time
+import urllib.parse
+from typing import Any, Dict, List, Optional, Union
+from unittest.mock import Mock
+from urllib.parse import urlencode
+
+import pymacaroons
+
+from twisted.web.resource import Resource
+
+import synapse.rest.admin
+from synapse.appservice import ApplicationService
+from synapse.rest.client import devices, login, logout, register
+from synapse.rest.client.account import WhoamiRestServlet
+from synapse.rest.synapse.client import build_synapse_client_resource_tree
+from synapse.types import create_requester
+
+from tests import unittest
+from tests.handlers.test_oidc import HAS_OIDC
+from tests.handlers.test_saml import has_saml2
+from tests.rest.client.utils import TEST_OIDC_AUTH_ENDPOINT, TEST_OIDC_CONFIG
+from tests.test_utils.html_parsers import TestHtmlParser
+from tests.unittest import HomeserverTestCase, override_config, skip_unless
+
+try:
+    import jwt
+
+    HAS_JWT = True
+except ImportError:
+    HAS_JWT = False
+
+
+# synapse server name: used to populate public_baseurl in some tests
+SYNAPSE_SERVER_PUBLIC_HOSTNAME = "synapse"
+
+# public_baseurl for some tests. It uses an http:// scheme because
+# FakeChannel.isSecure() returns False, so synapse will see the requested uri as
+# http://..., so using http in the public_baseurl stops Synapse trying to redirect to
+# https://....
+BASE_URL = "http://%s/" % (SYNAPSE_SERVER_PUBLIC_HOSTNAME,)
+
+# CAS server used in some tests
+CAS_SERVER = "https://fake.test"
+
+# just enough to tell pysaml2 where to redirect to
+SAML_SERVER = "https://test.saml.server/idp/sso"
+TEST_SAML_METADATA = """
+<md:EntityDescriptor xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata">
+  <md:IDPSSODescriptor protocolSupportEnumeration="urn:oasis:names:tc:SAML:2.0:protocol">
+      <md:SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect" Location="%(SAML_SERVER)s"/>
+  </md:IDPSSODescriptor>
+</md:EntityDescriptor>
+""" % {
+    "SAML_SERVER": SAML_SERVER,
+}
+
+LOGIN_URL = b"/_matrix/client/r0/login"
+TEST_URL = b"/_matrix/client/r0/account/whoami"
+
+# a (valid) url with some annoying characters in.  %3D is =, %26 is &, %2B is +
+TEST_CLIENT_REDIRECT_URL = 'https://x?<ab c>&q"+%3D%2B"="fö%26=o"'
+
+# the query params in TEST_CLIENT_REDIRECT_URL
+EXPECTED_CLIENT_REDIRECT_URL_PARAMS = [("<ab c>", ""), ('q" =+"', '"fö&=o"')]
+
+# (possibly experimental) login flows we expect to appear in the list after the normal
+# ones
+ADDITIONAL_LOGIN_FLOWS = [{"type": "uk.half-shot.msc2778.login.application_service"}]
+
+
+class LoginRestServletTestCase(unittest.HomeserverTestCase):
+
+    servlets = [
+        synapse.rest.admin.register_servlets_for_client_rest_resource,
+        login.register_servlets,
+        logout.register_servlets,
+        devices.register_servlets,
+        lambda hs, http_server: WhoamiRestServlet(hs).register(http_server),
+    ]
+
+    def make_homeserver(self, reactor, clock):
+        self.hs = self.setup_test_homeserver()
+        self.hs.config.enable_registration = True
+        self.hs.config.registrations_require_3pid = []
+        self.hs.config.auto_join_rooms = []
+        self.hs.config.enable_registration_captcha = False
+
+        return self.hs
+
+    @override_config(
+        {
+            "rc_login": {
+                "address": {"per_second": 0.17, "burst_count": 5},
+                # Prevent the account login ratelimiter from raising first
+                #
+                # This is normally covered by the default test homeserver config
+                # which sets these values to 10000, but as we're overriding the entire
+                # rc_login dict here, we need to set this manually as well
+                "account": {"per_second": 10000, "burst_count": 10000},
+            }
+        }
+    )
+    def test_POST_ratelimiting_per_address(self):
+        # Create different users so we're sure not to be bothered by the per-user
+        # ratelimiter.
+        for i in range(0, 6):
+            self.register_user("kermit" + str(i), "monkey")
+
+        for i in range(0, 6):
+            params = {
+                "type": "m.login.password",
+                "identifier": {"type": "m.id.user", "user": "kermit" + str(i)},
+                "password": "monkey",
+            }
+            channel = self.make_request(b"POST", LOGIN_URL, params)
+
+            if i == 5:
+                self.assertEquals(channel.result["code"], b"429", channel.result)
+                retry_after_ms = int(channel.json_body["retry_after_ms"])
+            else:
+                self.assertEquals(channel.result["code"], b"200", channel.result)
+
+        # Since we're ratelimiting at 1 request/min, retry_after_ms should be lower
+        # than 1min.
+        self.assertTrue(retry_after_ms < 6000)
+
+        self.reactor.advance(retry_after_ms / 1000.0 + 1.0)
+
+        params = {
+            "type": "m.login.password",
+            "identifier": {"type": "m.id.user", "user": "kermit" + str(i)},
+            "password": "monkey",
+        }
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+
+        self.assertEquals(channel.result["code"], b"200", channel.result)
+
+    @override_config(
+        {
+            "rc_login": {
+                "account": {"per_second": 0.17, "burst_count": 5},
+                # Prevent the address login ratelimiter from raising first
+                #
+                # This is normally covered by the default test homeserver config
+                # which sets these values to 10000, but as we're overriding the entire
+                # rc_login dict here, we need to set this manually as well
+                "address": {"per_second": 10000, "burst_count": 10000},
+            }
+        }
+    )
+    def test_POST_ratelimiting_per_account(self):
+        self.register_user("kermit", "monkey")
+
+        for i in range(0, 6):
+            params = {
+                "type": "m.login.password",
+                "identifier": {"type": "m.id.user", "user": "kermit"},
+                "password": "monkey",
+            }
+            channel = self.make_request(b"POST", LOGIN_URL, params)
+
+            if i == 5:
+                self.assertEquals(channel.result["code"], b"429", channel.result)
+                retry_after_ms = int(channel.json_body["retry_after_ms"])
+            else:
+                self.assertEquals(channel.result["code"], b"200", channel.result)
+
+        # Since we're ratelimiting at 1 request/min, retry_after_ms should be lower
+        # than 1min.
+        self.assertTrue(retry_after_ms < 6000)
+
+        self.reactor.advance(retry_after_ms / 1000.0)
+
+        params = {
+            "type": "m.login.password",
+            "identifier": {"type": "m.id.user", "user": "kermit"},
+            "password": "monkey",
+        }
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+
+        self.assertEquals(channel.result["code"], b"200", channel.result)
+
+    @override_config(
+        {
+            "rc_login": {
+                # Prevent the address login ratelimiter from raising first
+                #
+                # This is normally covered by the default test homeserver config
+                # which sets these values to 10000, but as we're overriding the entire
+                # rc_login dict here, we need to set this manually as well
+                "address": {"per_second": 10000, "burst_count": 10000},
+                "failed_attempts": {"per_second": 0.17, "burst_count": 5},
+            }
+        }
+    )
+    def test_POST_ratelimiting_per_account_failed_attempts(self):
+        self.register_user("kermit", "monkey")
+
+        for i in range(0, 6):
+            params = {
+                "type": "m.login.password",
+                "identifier": {"type": "m.id.user", "user": "kermit"},
+                "password": "notamonkey",
+            }
+            channel = self.make_request(b"POST", LOGIN_URL, params)
+
+            if i == 5:
+                self.assertEquals(channel.result["code"], b"429", channel.result)
+                retry_after_ms = int(channel.json_body["retry_after_ms"])
+            else:
+                self.assertEquals(channel.result["code"], b"403", channel.result)
+
+        # Since we're ratelimiting at 1 request/min, retry_after_ms should be lower
+        # than 1min.
+        self.assertTrue(retry_after_ms < 6000)
+
+        self.reactor.advance(retry_after_ms / 1000.0 + 1.0)
+
+        params = {
+            "type": "m.login.password",
+            "identifier": {"type": "m.id.user", "user": "kermit"},
+            "password": "notamonkey",
+        }
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+
+        self.assertEquals(channel.result["code"], b"403", channel.result)
+
+    @override_config({"session_lifetime": "24h"})
+    def test_soft_logout(self):
+        self.register_user("kermit", "monkey")
+
+        # we shouldn't be able to make requests without an access token
+        channel = self.make_request(b"GET", TEST_URL)
+        self.assertEquals(channel.result["code"], b"401", channel.result)
+        self.assertEquals(channel.json_body["errcode"], "M_MISSING_TOKEN")
+
+        # log in as normal
+        params = {
+            "type": "m.login.password",
+            "identifier": {"type": "m.id.user", "user": "kermit"},
+            "password": "monkey",
+        }
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+
+        self.assertEquals(channel.code, 200, channel.result)
+        access_token = channel.json_body["access_token"]
+        device_id = channel.json_body["device_id"]
+
+        # we should now be able to make requests with the access token
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 200, channel.result)
+
+        # time passes
+        self.reactor.advance(24 * 3600)
+
+        # ... and we should be soft-logouted
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 401, channel.result)
+        self.assertEquals(channel.json_body["errcode"], "M_UNKNOWN_TOKEN")
+        self.assertEquals(channel.json_body["soft_logout"], True)
+
+        #
+        # test behaviour after deleting the expired device
+        #
+
+        # we now log in as a different device
+        access_token_2 = self.login("kermit", "monkey")
+
+        # more requests with the expired token should still return a soft-logout
+        self.reactor.advance(3600)
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 401, channel.result)
+        self.assertEquals(channel.json_body["errcode"], "M_UNKNOWN_TOKEN")
+        self.assertEquals(channel.json_body["soft_logout"], True)
+
+        # ... but if we delete that device, it will be a proper logout
+        self._delete_device(access_token_2, "kermit", "monkey", device_id)
+
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 401, channel.result)
+        self.assertEquals(channel.json_body["errcode"], "M_UNKNOWN_TOKEN")
+        self.assertEquals(channel.json_body["soft_logout"], False)
+
+    def _delete_device(self, access_token, user_id, password, device_id):
+        """Perform the UI-Auth to delete a device"""
+        channel = self.make_request(
+            b"DELETE", "devices/" + device_id, access_token=access_token
+        )
+        self.assertEquals(channel.code, 401, channel.result)
+        # check it's a UI-Auth fail
+        self.assertEqual(
+            set(channel.json_body.keys()),
+            {"flows", "params", "session"},
+            channel.result,
+        )
+
+        auth = {
+            "type": "m.login.password",
+            # https://github.com/matrix-org/synapse/issues/5665
+            # "identifier": {"type": "m.id.user", "user": user_id},
+            "user": user_id,
+            "password": password,
+            "session": channel.json_body["session"],
+        }
+
+        channel = self.make_request(
+            b"DELETE",
+            "devices/" + device_id,
+            access_token=access_token,
+            content={"auth": auth},
+        )
+        self.assertEquals(channel.code, 200, channel.result)
+
+    @override_config({"session_lifetime": "24h"})
+    def test_session_can_hard_logout_after_being_soft_logged_out(self):
+        self.register_user("kermit", "monkey")
+
+        # log in as normal
+        access_token = self.login("kermit", "monkey")
+
+        # we should now be able to make requests with the access token
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 200, channel.result)
+
+        # time passes
+        self.reactor.advance(24 * 3600)
+
+        # ... and we should be soft-logouted
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 401, channel.result)
+        self.assertEquals(channel.json_body["errcode"], "M_UNKNOWN_TOKEN")
+        self.assertEquals(channel.json_body["soft_logout"], True)
+
+        # Now try to hard logout this session
+        channel = self.make_request(b"POST", "/logout", access_token=access_token)
+        self.assertEquals(channel.result["code"], b"200", channel.result)
+
+    @override_config({"session_lifetime": "24h"})
+    def test_session_can_hard_logout_all_sessions_after_being_soft_logged_out(self):
+        self.register_user("kermit", "monkey")
+
+        # log in as normal
+        access_token = self.login("kermit", "monkey")
+
+        # we should now be able to make requests with the access token
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 200, channel.result)
+
+        # time passes
+        self.reactor.advance(24 * 3600)
+
+        # ... and we should be soft-logouted
+        channel = self.make_request(b"GET", TEST_URL, access_token=access_token)
+        self.assertEquals(channel.code, 401, channel.result)
+        self.assertEquals(channel.json_body["errcode"], "M_UNKNOWN_TOKEN")
+        self.assertEquals(channel.json_body["soft_logout"], True)
+
+        # Now try to hard log out all of the user's sessions
+        channel = self.make_request(b"POST", "/logout/all", access_token=access_token)
+        self.assertEquals(channel.result["code"], b"200", channel.result)
+
+
+@skip_unless(has_saml2 and HAS_OIDC, "Requires SAML2 and OIDC")
+class MultiSSOTestCase(unittest.HomeserverTestCase):
+    """Tests for homeservers with multiple SSO providers enabled"""
+
+    servlets = [
+        login.register_servlets,
+    ]
+
+    def default_config(self) -> Dict[str, Any]:
+        config = super().default_config()
+
+        config["public_baseurl"] = BASE_URL
+
+        config["cas_config"] = {
+            "enabled": True,
+            "server_url": CAS_SERVER,
+            "service_url": "https://matrix.goodserver.com:8448",
+        }
+
+        config["saml2_config"] = {
+            "sp_config": {
+                "metadata": {"inline": [TEST_SAML_METADATA]},
+                # use the XMLSecurity backend to avoid relying on xmlsec1
+                "crypto_backend": "XMLSecurity",
+            },
+        }
+
+        # default OIDC provider
+        config["oidc_config"] = TEST_OIDC_CONFIG
+
+        # additional OIDC providers
+        config["oidc_providers"] = [
+            {
+                "idp_id": "idp1",
+                "idp_name": "IDP1",
+                "discover": False,
+                "issuer": "https://issuer1",
+                "client_id": "test-client-id",
+                "client_secret": "test-client-secret",
+                "scopes": ["profile"],
+                "authorization_endpoint": "https://issuer1/auth",
+                "token_endpoint": "https://issuer1/token",
+                "userinfo_endpoint": "https://issuer1/userinfo",
+                "user_mapping_provider": {
+                    "config": {"localpart_template": "{{ user.sub }}"}
+                },
+            }
+        ]
+        return config
+
+    def create_resource_dict(self) -> Dict[str, Resource]:
+        d = super().create_resource_dict()
+        d.update(build_synapse_client_resource_tree(self.hs))
+        return d
+
+    def test_get_login_flows(self):
+        """GET /login should return password and SSO flows"""
+        channel = self.make_request("GET", "/_matrix/client/r0/login")
+        self.assertEqual(channel.code, 200, channel.result)
+
+        expected_flow_types = [
+            "m.login.cas",
+            "m.login.sso",
+            "m.login.token",
+            "m.login.password",
+        ] + [f["type"] for f in ADDITIONAL_LOGIN_FLOWS]
+
+        self.assertCountEqual(
+            [f["type"] for f in channel.json_body["flows"]], expected_flow_types
+        )
+
+    @override_config({"experimental_features": {"msc2858_enabled": True}})
+    def test_get_msc2858_login_flows(self):
+        """The SSO flow should include IdP info if MSC2858 is enabled"""
+        channel = self.make_request("GET", "/_matrix/client/r0/login")
+        self.assertEqual(channel.code, 200, channel.result)
+
+        # stick the flows results in a dict by type
+        flow_results: Dict[str, Any] = {}
+        for f in channel.json_body["flows"]:
+            flow_type = f["type"]
+            self.assertNotIn(
+                flow_type, flow_results, "duplicate flow type %s" % (flow_type,)
+            )
+            flow_results[flow_type] = f
+
+        self.assertIn("m.login.sso", flow_results, "m.login.sso was not returned")
+        sso_flow = flow_results.pop("m.login.sso")
+        # we should have a set of IdPs
+        self.assertCountEqual(
+            sso_flow["org.matrix.msc2858.identity_providers"],
+            [
+                {"id": "cas", "name": "CAS"},
+                {"id": "saml", "name": "SAML"},
+                {"id": "oidc-idp1", "name": "IDP1"},
+                {"id": "oidc", "name": "OIDC"},
+            ],
+        )
+
+        # the rest of the flows are simple
+        expected_flows = [
+            {"type": "m.login.cas"},
+            {"type": "m.login.token"},
+            {"type": "m.login.password"},
+        ] + ADDITIONAL_LOGIN_FLOWS
+
+        self.assertCountEqual(flow_results.values(), expected_flows)
+
+    def test_multi_sso_redirect(self):
+        """/login/sso/redirect should redirect to an identity picker"""
+        # first hit the redirect url, which should redirect to our idp picker
+        channel = self._make_sso_redirect_request(False, None)
+        self.assertEqual(channel.code, 302, channel.result)
+        uri = channel.headers.getRawHeaders("Location")[0]
+
+        # hitting that picker should give us some HTML
+        channel = self.make_request("GET", uri)
+        self.assertEqual(channel.code, 200, channel.result)
+
+        # parse the form to check it has fields assumed elsewhere in this class
+        html = channel.result["body"].decode("utf-8")
+        p = TestHtmlParser()
+        p.feed(html)
+        p.close()
+
+        # there should be a link for each href
+        returned_idps: List[str] = []
+        for link in p.links:
+            path, query = link.split("?", 1)
+            self.assertEqual(path, "pick_idp")
+            params = urllib.parse.parse_qs(query)
+            self.assertEqual(params["redirectUrl"], [TEST_CLIENT_REDIRECT_URL])
+            returned_idps.append(params["idp"][0])
+
+        self.assertCountEqual(returned_idps, ["cas", "oidc", "oidc-idp1", "saml"])
+
+    def test_multi_sso_redirect_to_cas(self):
+        """If CAS is chosen, should redirect to the CAS server"""
+
+        channel = self.make_request(
+            "GET",
+            "/_synapse/client/pick_idp?redirectUrl="
+            + urllib.parse.quote_plus(TEST_CLIENT_REDIRECT_URL)
+            + "&idp=cas",
+            shorthand=False,
+        )
+        self.assertEqual(channel.code, 302, channel.result)
+        location_headers = channel.headers.getRawHeaders("Location")
+        assert location_headers
+        cas_uri = location_headers[0]
+        cas_uri_path, cas_uri_query = cas_uri.split("?", 1)
+
+        # it should redirect us to the login page of the cas server
+        self.assertEqual(cas_uri_path, CAS_SERVER + "/login")
+
+        # check that the redirectUrl is correctly encoded in the service param - ie, the
+        # place that CAS will redirect to
+        cas_uri_params = urllib.parse.parse_qs(cas_uri_query)
+        service_uri = cas_uri_params["service"][0]
+        _, service_uri_query = service_uri.split("?", 1)
+        service_uri_params = urllib.parse.parse_qs(service_uri_query)
+        self.assertEqual(service_uri_params["redirectUrl"][0], TEST_CLIENT_REDIRECT_URL)
+
+    def test_multi_sso_redirect_to_saml(self):
+        """If SAML is chosen, should redirect to the SAML server"""
+        channel = self.make_request(
+            "GET",
+            "/_synapse/client/pick_idp?redirectUrl="
+            + urllib.parse.quote_plus(TEST_CLIENT_REDIRECT_URL)
+            + "&idp=saml",
+        )
+        self.assertEqual(channel.code, 302, channel.result)
+        location_headers = channel.headers.getRawHeaders("Location")
+        assert location_headers
+        saml_uri = location_headers[0]
+        saml_uri_path, saml_uri_query = saml_uri.split("?", 1)
+
+        # it should redirect us to the login page of the SAML server
+        self.assertEqual(saml_uri_path, SAML_SERVER)
+
+        # the RelayState is used to carry the client redirect url
+        saml_uri_params = urllib.parse.parse_qs(saml_uri_query)
+        relay_state_param = saml_uri_params["RelayState"][0]
+        self.assertEqual(relay_state_param, TEST_CLIENT_REDIRECT_URL)
+
+    def test_login_via_oidc(self):
+        """If OIDC is chosen, should redirect to the OIDC auth endpoint"""
+
+        # pick the default OIDC provider
+        channel = self.make_request(
+            "GET",
+            "/_synapse/client/pick_idp?redirectUrl="
+            + urllib.parse.quote_plus(TEST_CLIENT_REDIRECT_URL)
+            + "&idp=oidc",
+        )
+        self.assertEqual(channel.code, 302, channel.result)
+        location_headers = channel.headers.getRawHeaders("Location")
+        assert location_headers
+        oidc_uri = location_headers[0]
+        oidc_uri_path, oidc_uri_query = oidc_uri.split("?", 1)
+
+        # it should redirect us to the auth page of the OIDC server
+        self.assertEqual(oidc_uri_path, TEST_OIDC_AUTH_ENDPOINT)
+
+        # ... and should have set a cookie including the redirect url
+        cookie_headers = channel.headers.getRawHeaders("Set-Cookie")
+        assert cookie_headers
+        cookies: Dict[str, str] = {}
+        for h in cookie_headers:
+            key, value = h.split(";")[0].split("=", maxsplit=1)
+            cookies[key] = value
+
+        oidc_session_cookie = cookies["oidc_session"]
+        macaroon = pymacaroons.Macaroon.deserialize(oidc_session_cookie)
+        self.assertEqual(
+            self._get_value_from_macaroon(macaroon, "client_redirect_url"),
+            TEST_CLIENT_REDIRECT_URL,
+        )
+
+        channel = self.helper.complete_oidc_auth(oidc_uri, cookies, {"sub": "user1"})
+
+        # that should serve a confirmation page
+        self.assertEqual(channel.code, 200, channel.result)
+        content_type_headers = channel.headers.getRawHeaders("Content-Type")
+        assert content_type_headers
+        self.assertTrue(content_type_headers[-1].startswith("text/html"))
+        p = TestHtmlParser()
+        p.feed(channel.text_body)
+        p.close()
+
+        # ... which should contain our redirect link
+        self.assertEqual(len(p.links), 1)
+        path, query = p.links[0].split("?", 1)
+        self.assertEqual(path, "https://x")
+
+        # it will have url-encoded the params properly, so we'll have to parse them
+        params = urllib.parse.parse_qsl(
+            query, keep_blank_values=True, strict_parsing=True, errors="strict"
+        )
+        self.assertEqual(params[0:2], EXPECTED_CLIENT_REDIRECT_URL_PARAMS)
+        self.assertEqual(params[2][0], "loginToken")
+
+        # finally, submit the matrix login token to the login API, which gives us our
+        # matrix access token, mxid, and device id.
+        login_token = params[2][1]
+        chan = self.make_request(
+            "POST",
+            "/login",
+            content={"type": "m.login.token", "token": login_token},
+        )
+        self.assertEqual(chan.code, 200, chan.result)
+        self.assertEqual(chan.json_body["user_id"], "@user1:test")
+
+    def test_multi_sso_redirect_to_unknown(self):
+        """An unknown IdP should cause a 400"""
+        channel = self.make_request(
+            "GET",
+            "/_synapse/client/pick_idp?redirectUrl=http://x&idp=xyz",
+        )
+        self.assertEqual(channel.code, 400, channel.result)
+
+    def test_client_idp_redirect_to_unknown(self):
+        """If the client tries to pick an unknown IdP, return a 404"""
+        channel = self._make_sso_redirect_request(False, "xxx")
+        self.assertEqual(channel.code, 404, channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_NOT_FOUND")
+
+    def test_client_idp_redirect_to_oidc(self):
+        """If the client pick a known IdP, redirect to it"""
+        channel = self._make_sso_redirect_request(False, "oidc")
+        self.assertEqual(channel.code, 302, channel.result)
+        oidc_uri = channel.headers.getRawHeaders("Location")[0]
+        oidc_uri_path, oidc_uri_query = oidc_uri.split("?", 1)
+
+        # it should redirect us to the auth page of the OIDC server
+        self.assertEqual(oidc_uri_path, TEST_OIDC_AUTH_ENDPOINT)
+
+    @override_config({"experimental_features": {"msc2858_enabled": True}})
+    def test_client_msc2858_redirect_to_oidc(self):
+        """Test the unstable API"""
+        channel = self._make_sso_redirect_request(True, "oidc")
+        self.assertEqual(channel.code, 302, channel.result)
+        oidc_uri = channel.headers.getRawHeaders("Location")[0]
+        oidc_uri_path, oidc_uri_query = oidc_uri.split("?", 1)
+
+        # it should redirect us to the auth page of the OIDC server
+        self.assertEqual(oidc_uri_path, TEST_OIDC_AUTH_ENDPOINT)
+
+    def test_client_idp_redirect_msc2858_disabled(self):
+        """If the client tries to use the MSC2858 endpoint but MSC2858 is disabled, return a 400"""
+        channel = self._make_sso_redirect_request(True, "oidc")
+        self.assertEqual(channel.code, 400, channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_UNRECOGNIZED")
+
+    def _make_sso_redirect_request(
+        self, unstable_endpoint: bool = False, idp_prov: Optional[str] = None
+    ):
+        """Send a request to /_matrix/client/r0/login/sso/redirect
+
+        ... or the unstable equivalent
+
+        ... possibly specifying an IDP provider
+        """
+        endpoint = (
+            "/_matrix/client/unstable/org.matrix.msc2858/login/sso/redirect"
+            if unstable_endpoint
+            else "/_matrix/client/r0/login/sso/redirect"
+        )
+        if idp_prov is not None:
+            endpoint += "/" + idp_prov
+        endpoint += "?redirectUrl=" + urllib.parse.quote_plus(TEST_CLIENT_REDIRECT_URL)
+
+        return self.make_request(
+            "GET",
+            endpoint,
+            custom_headers=[("Host", SYNAPSE_SERVER_PUBLIC_HOSTNAME)],
+        )
+
+    @staticmethod
+    def _get_value_from_macaroon(macaroon: pymacaroons.Macaroon, key: str) -> str:
+        prefix = key + " = "
+        for caveat in macaroon.caveats:
+            if caveat.caveat_id.startswith(prefix):
+                return caveat.caveat_id[len(prefix) :]
+        raise ValueError("No %s caveat in macaroon" % (key,))
+
+
+class CASTestCase(unittest.HomeserverTestCase):
+
+    servlets = [
+        login.register_servlets,
+    ]
+
+    def make_homeserver(self, reactor, clock):
+        self.base_url = "https://matrix.goodserver.com/"
+        self.redirect_path = "_synapse/client/login/sso/redirect/confirm"
+
+        config = self.default_config()
+        config["public_baseurl"] = (
+            config.get("public_baseurl") or "https://matrix.goodserver.com:8448"
+        )
+        config["cas_config"] = {
+            "enabled": True,
+            "server_url": CAS_SERVER,
+        }
+
+        cas_user_id = "username"
+        self.user_id = "@%s:test" % cas_user_id
+
+        async def get_raw(uri, args):
+            """Return an example response payload from a call to the `/proxyValidate`
+            endpoint of a CAS server, copied from
+            https://apereo.github.io/cas/5.0.x/protocol/CAS-Protocol-V2-Specification.html#26-proxyvalidate-cas-20
+
+            This needs to be returned by an async function (as opposed to set as the
+            mock's return value) because the corresponding Synapse code awaits on it.
+            """
+            return (
+                """
+                <cas:serviceResponse xmlns:cas='http://www.yale.edu/tp/cas'>
+                  <cas:authenticationSuccess>
+                      <cas:user>%s</cas:user>
+                      <cas:proxyGrantingTicket>PGTIOU-84678-8a9d...</cas:proxyGrantingTicket>
+                      <cas:proxies>
+                          <cas:proxy>https://proxy2/pgtUrl</cas:proxy>
+                          <cas:proxy>https://proxy1/pgtUrl</cas:proxy>
+                      </cas:proxies>
+                  </cas:authenticationSuccess>
+                </cas:serviceResponse>
+            """
+                % cas_user_id
+            ).encode("utf-8")
+
+        mocked_http_client = Mock(spec=["get_raw"])
+        mocked_http_client.get_raw.side_effect = get_raw
+
+        self.hs = self.setup_test_homeserver(
+            config=config,
+            proxied_http_client=mocked_http_client,
+        )
+
+        return self.hs
+
+    def prepare(self, reactor, clock, hs):
+        self.deactivate_account_handler = hs.get_deactivate_account_handler()
+
+    def test_cas_redirect_confirm(self):
+        """Tests that the SSO login flow serves a confirmation page before redirecting a
+        user to the redirect URL.
+        """
+        base_url = "/_matrix/client/r0/login/cas/ticket?redirectUrl"
+        redirect_url = "https://dodgy-site.com/"
+
+        url_parts = list(urllib.parse.urlparse(base_url))
+        query = dict(urllib.parse.parse_qsl(url_parts[4]))
+        query.update({"redirectUrl": redirect_url})
+        query.update({"ticket": "ticket"})
+        url_parts[4] = urllib.parse.urlencode(query)
+        cas_ticket_url = urllib.parse.urlunparse(url_parts)
+
+        # Get Synapse to call the fake CAS and serve the template.
+        channel = self.make_request("GET", cas_ticket_url)
+
+        # Test that the response is HTML.
+        self.assertEqual(channel.code, 200, channel.result)
+        content_type_header_value = ""
+        for header in channel.result.get("headers", []):
+            if header[0] == b"Content-Type":
+                content_type_header_value = header[1].decode("utf8")
+
+        self.assertTrue(content_type_header_value.startswith("text/html"))
+
+        # Test that the body isn't empty.
+        self.assertTrue(len(channel.result["body"]) > 0)
+
+        # And that it contains our redirect link
+        self.assertIn(redirect_url, channel.result["body"].decode("UTF-8"))
+
+    @override_config(
+        {
+            "sso": {
+                "client_whitelist": [
+                    "https://legit-site.com/",
+                    "https://other-site.com/",
+                ]
+            }
+        }
+    )
+    def test_cas_redirect_whitelisted(self):
+        """Tests that the SSO login flow serves a redirect to a whitelisted url"""
+        self._test_redirect("https://legit-site.com/")
+
+    @override_config({"public_baseurl": "https://example.com"})
+    def test_cas_redirect_login_fallback(self):
+        self._test_redirect("https://example.com/_matrix/static/client/login")
+
+    def _test_redirect(self, redirect_url):
+        """Tests that the SSO login flow serves a redirect for the given redirect URL."""
+        cas_ticket_url = (
+            "/_matrix/client/r0/login/cas/ticket?redirectUrl=%s&ticket=ticket"
+            % (urllib.parse.quote(redirect_url))
+        )
+
+        # Get Synapse to call the fake CAS and serve the template.
+        channel = self.make_request("GET", cas_ticket_url)
+
+        self.assertEqual(channel.code, 302)
+        location_headers = channel.headers.getRawHeaders("Location")
+        assert location_headers
+        self.assertEqual(location_headers[0][: len(redirect_url)], redirect_url)
+
+    @override_config({"sso": {"client_whitelist": ["https://legit-site.com/"]}})
+    def test_deactivated_user(self):
+        """Logging in as a deactivated account should error."""
+        redirect_url = "https://legit-site.com/"
+
+        # First login (to create the user).
+        self._test_redirect(redirect_url)
+
+        # Deactivate the account.
+        self.get_success(
+            self.deactivate_account_handler.deactivate_account(
+                self.user_id, False, create_requester(self.user_id)
+            )
+        )
+
+        # Request the CAS ticket.
+        cas_ticket_url = (
+            "/_matrix/client/r0/login/cas/ticket?redirectUrl=%s&ticket=ticket"
+            % (urllib.parse.quote(redirect_url))
+        )
+
+        # Get Synapse to call the fake CAS and serve the template.
+        channel = self.make_request("GET", cas_ticket_url)
+
+        # Because the user is deactivated they are served an error template.
+        self.assertEqual(channel.code, 403)
+        self.assertIn(b"SSO account deactivated", channel.result["body"])
+
+
+@skip_unless(HAS_JWT, "requires jwt")
+class JWTTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        synapse.rest.admin.register_servlets_for_client_rest_resource,
+        login.register_servlets,
+    ]
+
+    jwt_secret = "secret"
+    jwt_algorithm = "HS256"
+
+    def make_homeserver(self, reactor, clock):
+        self.hs = self.setup_test_homeserver()
+        self.hs.config.jwt_enabled = True
+        self.hs.config.jwt_secret = self.jwt_secret
+        self.hs.config.jwt_algorithm = self.jwt_algorithm
+        return self.hs
+
+    def jwt_encode(self, payload: Dict[str, Any], secret: str = jwt_secret) -> str:
+        # PyJWT 2.0.0 changed the return type of jwt.encode from bytes to str.
+        result: Union[str, bytes] = jwt.encode(payload, secret, self.jwt_algorithm)
+        if isinstance(result, bytes):
+            return result.decode("ascii")
+        return result
+
+    def jwt_login(self, *args):
+        params = {"type": "org.matrix.login.jwt", "token": self.jwt_encode(*args)}
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+        return channel
+
+    def test_login_jwt_valid_registered(self):
+        self.register_user("kermit", "monkey")
+        channel = self.jwt_login({"sub": "kermit"})
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        self.assertEqual(channel.json_body["user_id"], "@kermit:test")
+
+    def test_login_jwt_valid_unregistered(self):
+        channel = self.jwt_login({"sub": "frog"})
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        self.assertEqual(channel.json_body["user_id"], "@frog:test")
+
+    def test_login_jwt_invalid_signature(self):
+        channel = self.jwt_login({"sub": "frog"}, "notsecret")
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"],
+            "JWT validation failed: Signature verification failed",
+        )
+
+    def test_login_jwt_expired(self):
+        channel = self.jwt_login({"sub": "frog", "exp": 864000})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"], "JWT validation failed: Signature has expired"
+        )
+
+    def test_login_jwt_not_before(self):
+        now = int(time.time())
+        channel = self.jwt_login({"sub": "frog", "nbf": now + 3600})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"],
+            "JWT validation failed: The token is not yet valid (nbf)",
+        )
+
+    def test_login_no_sub(self):
+        channel = self.jwt_login({"username": "root"})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(channel.json_body["error"], "Invalid JWT")
+
+    @override_config(
+        {
+            "jwt_config": {
+                "jwt_enabled": True,
+                "secret": jwt_secret,
+                "algorithm": jwt_algorithm,
+                "issuer": "test-issuer",
+            }
+        }
+    )
+    def test_login_iss(self):
+        """Test validating the issuer claim."""
+        # A valid issuer.
+        channel = self.jwt_login({"sub": "kermit", "iss": "test-issuer"})
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        self.assertEqual(channel.json_body["user_id"], "@kermit:test")
+
+        # An invalid issuer.
+        channel = self.jwt_login({"sub": "kermit", "iss": "invalid"})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"], "JWT validation failed: Invalid issuer"
+        )
+
+        # Not providing an issuer.
+        channel = self.jwt_login({"sub": "kermit"})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"],
+            'JWT validation failed: Token is missing the "iss" claim',
+        )
+
+    def test_login_iss_no_config(self):
+        """Test providing an issuer claim without requiring it in the configuration."""
+        channel = self.jwt_login({"sub": "kermit", "iss": "invalid"})
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        self.assertEqual(channel.json_body["user_id"], "@kermit:test")
+
+    @override_config(
+        {
+            "jwt_config": {
+                "jwt_enabled": True,
+                "secret": jwt_secret,
+                "algorithm": jwt_algorithm,
+                "audiences": ["test-audience"],
+            }
+        }
+    )
+    def test_login_aud(self):
+        """Test validating the audience claim."""
+        # A valid audience.
+        channel = self.jwt_login({"sub": "kermit", "aud": "test-audience"})
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        self.assertEqual(channel.json_body["user_id"], "@kermit:test")
+
+        # An invalid audience.
+        channel = self.jwt_login({"sub": "kermit", "aud": "invalid"})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"], "JWT validation failed: Invalid audience"
+        )
+
+        # Not providing an audience.
+        channel = self.jwt_login({"sub": "kermit"})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"],
+            'JWT validation failed: Token is missing the "aud" claim',
+        )
+
+    def test_login_aud_no_config(self):
+        """Test providing an audience without requiring it in the configuration."""
+        channel = self.jwt_login({"sub": "kermit", "aud": "invalid"})
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"], "JWT validation failed: Invalid audience"
+        )
+
+    def test_login_no_token(self):
+        params = {"type": "org.matrix.login.jwt"}
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(channel.json_body["error"], "Token field for JWT is missing")
+
+
+# The JWTPubKeyTestCase is a complement to JWTTestCase where we instead use
+# RSS256, with a public key configured in synapse as "jwt_secret", and tokens
+# signed by the private key.
+@skip_unless(HAS_JWT, "requires jwt")
+class JWTPubKeyTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        login.register_servlets,
+    ]
+
+    # This key's pubkey is used as the jwt_secret setting of synapse. Valid
+    # tokens are signed by this and validated using the pubkey. It is generated
+    # with `openssl genrsa 512` (not a secure way to generate real keys, but
+    # good enough for tests!)
+    jwt_privatekey = "\n".join(
+        [
+            "-----BEGIN RSA PRIVATE KEY-----",
+            "MIIBPAIBAAJBAM50f1Q5gsdmzifLstzLHb5NhfajiOt7TKO1vSEWdq7u9x8SMFiB",
+            "492RM9W/XFoh8WUfL9uL6Now6tPRDsWv3xsCAwEAAQJAUv7OOSOtiU+wzJq82rnk",
+            "yR4NHqt7XX8BvkZPM7/+EjBRanmZNSp5kYZzKVaZ/gTOM9+9MwlmhidrUOweKfB/",
+            "kQIhAPZwHazbjo7dYlJs7wPQz1vd+aHSEH+3uQKIysebkmm3AiEA1nc6mDdmgiUq",
+            "TpIN8A4MBKmfZMWTLq6z05y/qjKyxb0CIQDYJxCwTEenIaEa4PdoJl+qmXFasVDN",
+            "ZU0+XtNV7yul0wIhAMI9IhiStIjS2EppBa6RSlk+t1oxh2gUWlIh+YVQfZGRAiEA",
+            "tqBR7qLZGJ5CVKxWmNhJZGt1QHoUtOch8t9C4IdOZ2g=",
+            "-----END RSA PRIVATE KEY-----",
+        ]
+    )
+
+    # Generated with `openssl rsa -in foo.key -pubout`, with the the above
+    # private key placed in foo.key (jwt_privatekey).
+    jwt_pubkey = "\n".join(
+        [
+            "-----BEGIN PUBLIC KEY-----",
+            "MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAM50f1Q5gsdmzifLstzLHb5NhfajiOt7",
+            "TKO1vSEWdq7u9x8SMFiB492RM9W/XFoh8WUfL9uL6Now6tPRDsWv3xsCAwEAAQ==",
+            "-----END PUBLIC KEY-----",
+        ]
+    )
+
+    # This key is used to sign tokens that shouldn't be accepted by synapse.
+    # Generated just like jwt_privatekey.
+    bad_privatekey = "\n".join(
+        [
+            "-----BEGIN RSA PRIVATE KEY-----",
+            "MIIBOgIBAAJBAL//SQrKpKbjCCnv/FlasJCv+t3k/MPsZfniJe4DVFhsktF2lwQv",
+            "gLjmQD3jBUTz+/FndLSBvr3F4OHtGL9O/osCAwEAAQJAJqH0jZJW7Smzo9ShP02L",
+            "R6HRZcLExZuUrWI+5ZSP7TaZ1uwJzGFspDrunqaVoPobndw/8VsP8HFyKtceC7vY",
+            "uQIhAPdYInDDSJ8rFKGiy3Ajv5KWISBicjevWHF9dbotmNO9AiEAxrdRJVU+EI9I",
+            "eB4qRZpY6n4pnwyP0p8f/A3NBaQPG+cCIFlj08aW/PbxNdqYoBdeBA0xDrXKfmbb",
+            "iwYxBkwL0JCtAiBYmsi94sJn09u2Y4zpuCbJeDPKzWkbuwQh+W1fhIWQJQIhAKR0",
+            "KydN6cRLvphNQ9c/vBTdlzWxzcSxREpguC7F1J1m",
+            "-----END RSA PRIVATE KEY-----",
+        ]
+    )
+
+    def make_homeserver(self, reactor, clock):
+        self.hs = self.setup_test_homeserver()
+        self.hs.config.jwt_enabled = True
+        self.hs.config.jwt_secret = self.jwt_pubkey
+        self.hs.config.jwt_algorithm = "RS256"
+        return self.hs
+
+    def jwt_encode(self, payload: Dict[str, Any], secret: str = jwt_privatekey) -> str:
+        # PyJWT 2.0.0 changed the return type of jwt.encode from bytes to str.
+        result: Union[bytes, str] = jwt.encode(payload, secret, "RS256")
+        if isinstance(result, bytes):
+            return result.decode("ascii")
+        return result
+
+    def jwt_login(self, *args):
+        params = {"type": "org.matrix.login.jwt", "token": self.jwt_encode(*args)}
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+        return channel
+
+    def test_login_jwt_valid(self):
+        channel = self.jwt_login({"sub": "kermit"})
+        self.assertEqual(channel.result["code"], b"200", channel.result)
+        self.assertEqual(channel.json_body["user_id"], "@kermit:test")
+
+    def test_login_jwt_invalid_signature(self):
+        channel = self.jwt_login({"sub": "frog"}, self.bad_privatekey)
+        self.assertEqual(channel.result["code"], b"403", channel.result)
+        self.assertEqual(channel.json_body["errcode"], "M_FORBIDDEN")
+        self.assertEqual(
+            channel.json_body["error"],
+            "JWT validation failed: Signature verification failed",
+        )
+
+
+AS_USER = "as_user_alice"
+
+
+class AppserviceLoginRestServletTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        login.register_servlets,
+        register.register_servlets,
+    ]
+
+    def register_as_user(self, username):
+        self.make_request(
+            b"POST",
+            "/_matrix/client/r0/register?access_token=%s" % (self.service.token,),
+            {"username": username},
+        )
+
+    def make_homeserver(self, reactor, clock):
+        self.hs = self.setup_test_homeserver()
+
+        self.service = ApplicationService(
+            id="unique_identifier",
+            token="some_token",
+            hostname="example.com",
+            sender="@asbot:example.com",
+            namespaces={
+                ApplicationService.NS_USERS: [
+                    {"regex": r"@as_user.*", "exclusive": False}
+                ],
+                ApplicationService.NS_ROOMS: [],
+                ApplicationService.NS_ALIASES: [],
+            },
+        )
+        self.another_service = ApplicationService(
+            id="another__identifier",
+            token="another_token",
+            hostname="example.com",
+            sender="@as2bot:example.com",
+            namespaces={
+                ApplicationService.NS_USERS: [
+                    {"regex": r"@as2_user.*", "exclusive": False}
+                ],
+                ApplicationService.NS_ROOMS: [],
+                ApplicationService.NS_ALIASES: [],
+            },
+        )
+
+        self.hs.get_datastore().services_cache.append(self.service)
+        self.hs.get_datastore().services_cache.append(self.another_service)
+        return self.hs
+
+    def test_login_appservice_user(self):
+        """Test that an appservice user can use /login"""
+        self.register_as_user(AS_USER)
+
+        params = {
+            "type": login.LoginRestServlet.APPSERVICE_TYPE,
+            "identifier": {"type": "m.id.user", "user": AS_USER},
+        }
+        channel = self.make_request(
+            b"POST", LOGIN_URL, params, access_token=self.service.token
+        )
+
+        self.assertEquals(channel.result["code"], b"200", channel.result)
+
+    def test_login_appservice_user_bot(self):
+        """Test that the appservice bot can use /login"""
+        self.register_as_user(AS_USER)
+
+        params = {
+            "type": login.LoginRestServlet.APPSERVICE_TYPE,
+            "identifier": {"type": "m.id.user", "user": self.service.sender},
+        }
+        channel = self.make_request(
+            b"POST", LOGIN_URL, params, access_token=self.service.token
+        )
+
+        self.assertEquals(channel.result["code"], b"200", channel.result)
+
+    def test_login_appservice_wrong_user(self):
+        """Test that non-as users cannot login with the as token"""
+        self.register_as_user(AS_USER)
+
+        params = {
+            "type": login.LoginRestServlet.APPSERVICE_TYPE,
+            "identifier": {"type": "m.id.user", "user": "fibble_wibble"},
+        }
+        channel = self.make_request(
+            b"POST", LOGIN_URL, params, access_token=self.service.token
+        )
+
+        self.assertEquals(channel.result["code"], b"403", channel.result)
+
+    def test_login_appservice_wrong_as(self):
+        """Test that as users cannot login with wrong as token"""
+        self.register_as_user(AS_USER)
+
+        params = {
+            "type": login.LoginRestServlet.APPSERVICE_TYPE,
+            "identifier": {"type": "m.id.user", "user": AS_USER},
+        }
+        channel = self.make_request(
+            b"POST", LOGIN_URL, params, access_token=self.another_service.token
+        )
+
+        self.assertEquals(channel.result["code"], b"403", channel.result)
+
+    def test_login_appservice_no_token(self):
+        """Test that users must provide a token when using the appservice
+        login method
+        """
+        self.register_as_user(AS_USER)
+
+        params = {
+            "type": login.LoginRestServlet.APPSERVICE_TYPE,
+            "identifier": {"type": "m.id.user", "user": AS_USER},
+        }
+        channel = self.make_request(b"POST", LOGIN_URL, params)
+
+        self.assertEquals(channel.result["code"], b"401", channel.result)
+
+
+@skip_unless(HAS_OIDC, "requires OIDC")
+class UsernamePickerTestCase(HomeserverTestCase):
+    """Tests for the username picker flow of SSO login"""
+
+    servlets = [login.register_servlets]
+
+    def default_config(self):
+        config = super().default_config()
+        config["public_baseurl"] = BASE_URL
+
+        config["oidc_config"] = {}
+        config["oidc_config"].update(TEST_OIDC_CONFIG)
+        config["oidc_config"]["user_mapping_provider"] = {
+            "config": {"display_name_template": "{{ user.displayname }}"}
+        }
+
+        # whitelist this client URI so we redirect straight to it rather than
+        # serving a confirmation page
+        config["sso"] = {"client_whitelist": ["https://x"]}
+        return config
+
+    def create_resource_dict(self) -> Dict[str, Resource]:
+        d = super().create_resource_dict()
+        d.update(build_synapse_client_resource_tree(self.hs))
+        return d
+
+    def test_username_picker(self):
+        """Test the happy path of a username picker flow."""
+
+        # do the start of the login flow
+        channel = self.helper.auth_via_oidc(
+            {"sub": "tester", "displayname": "Jonny"}, TEST_CLIENT_REDIRECT_URL
+        )
+
+        # that should redirect to the username picker
+        self.assertEqual(channel.code, 302, channel.result)
+        location_headers = channel.headers.getRawHeaders("Location")
+        assert location_headers
+        picker_url = location_headers[0]
+        self.assertEqual(picker_url, "/_synapse/client/pick_username/account_details")
+
+        # ... with a username_mapping_session cookie
+        cookies: Dict[str, str] = {}
+        channel.extract_cookies(cookies)
+        self.assertIn("username_mapping_session", cookies)
+        session_id = cookies["username_mapping_session"]
+
+        # introspect the sso handler a bit to check that the username mapping session
+        # looks ok.
+        username_mapping_sessions = self.hs.get_sso_handler()._username_mapping_sessions
+        self.assertIn(
+            session_id,
+            username_mapping_sessions,
+            "session id not found in map",
+        )
+        session = username_mapping_sessions[session_id]
+        self.assertEqual(session.remote_user_id, "tester")
+        self.assertEqual(session.display_name, "Jonny")
+        self.assertEqual(session.client_redirect_url, TEST_CLIENT_REDIRECT_URL)
+
+        # the expiry time should be about 15 minutes away
+        expected_expiry = self.clock.time_msec() + (15 * 60 * 1000)
+        self.assertApproximates(session.expiry_time_ms, expected_expiry, tolerance=1000)
+
+        # Now, submit a username to the username picker, which should serve a redirect
+        # to the completion page
+        content = urlencode({b"username": b"bobby"}).encode("utf8")
+        chan = self.make_request(
+            "POST",
+            path=picker_url,
+            content=content,
+            content_is_form=True,
+            custom_headers=[
+                ("Cookie", "username_mapping_session=" + session_id),
+                # old versions of twisted don't do form-parsing without a valid
+                # content-length header.
+                ("Content-Length", str(len(content))),
+            ],
+        )
+        self.assertEqual(chan.code, 302, chan.result)
+        location_headers = chan.headers.getRawHeaders("Location")
+        assert location_headers
+
+        # send a request to the completion page, which should 302 to the client redirectUrl
+        chan = self.make_request(
+            "GET",
+            path=location_headers[0],
+            custom_headers=[("Cookie", "username_mapping_session=" + session_id)],
+        )
+        self.assertEqual(chan.code, 302, chan.result)
+        location_headers = chan.headers.getRawHeaders("Location")
+        assert location_headers
+
+        # ensure that the returned location matches the requested redirect URL
+        path, query = location_headers[0].split("?", 1)
+        self.assertEqual(path, "https://x")
+
+        # it will have url-encoded the params properly, so we'll have to parse them
+        params = urllib.parse.parse_qsl(
+            query, keep_blank_values=True, strict_parsing=True, errors="strict"
+        )
+        self.assertEqual(params[0:2], EXPECTED_CLIENT_REDIRECT_URL_PARAMS)
+        self.assertEqual(params[2][0], "loginToken")
+
+        # fish the login token out of the returned redirect uri
+        login_token = params[2][1]
+
+        # finally, submit the matrix login token to the login API, which gives us our
+        # matrix access token, mxid, and device id.
+        chan = self.make_request(
+            "POST",
+            "/login",
+            content={"type": "m.login.token", "token": login_token},
+        )
+        self.assertEqual(chan.code, 200, chan.result)
+        self.assertEqual(chan.json_body["user_id"], "@bobby:test")