feat: Allow multiple values for SSO attribute_requirements via comma separation (#17949)

In the current `attribute_requirements` implementation it is only
possible to allow exact matching attribute values. Multiple allowed
values for one attribute are not possible as described in #13238.

### Pull Request Checklist

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---------

Co-authored-by: Sebastian Neuser <pzkz@infra.run>
Co-authored-by: Quentin Gliech <quenting@element.io>

1 files changed, 15 insertions, 5 deletions

diff --git a/synapse/config/sso.py b/synapse/config/sso.py

index d7a2187e7d..97b85e47ea 100644
--- a/synapse/config/sso.py
+++ b/synapse/config/sso.py
@@ -19,7 +19,7 @@
 #
 #
 import logging
-from typing import Any, Dict, Optional
+from typing import Any, Dict, List, Optional
 
 import attr
 
@@ -43,13 +43,23 @@ class SsoAttributeRequirement:
     """Object describing a single requirement for SSO attributes."""
 
     attribute: str
-    # If a value is not given, than the attribute must simply exist.
-    value: Optional[str]
+    # If neither value nor one_of is given, the attribute must simply exist. This is
+    # only true for CAS configs which use a different JSON schema than the one below.
+    value: Optional[str] = None
+    one_of: Optional[List[str]] = None
 
     JSON_SCHEMA = {
         "type": "object",
-        "properties": {"attribute": {"type": "string"}, "value": {"type": "string"}},
-        "required": ["attribute", "value"],
+        "properties": {
+            "attribute": {"type": "string"},
+            "value": {"type": "string"},
+            "one_of": {"type": "array", "items": {"type": "string"}},
+        },
+        "required": ["attribute"],
+        "oneOf": [
+            {"required": ["value"]},
+            {"required": ["one_of"]},
+        ],
     }