Combine the SSO Redirect Servlets (#9015)

* Implement CasHandler.handle_redirect_request

... to make it match OidcHandler and SamlHandler

* Clean up interface for OidcHandler.handle_redirect_request

Make it accept `client_redirect_url=None`.

* Clean up interface for `SamlHandler.handle_redirect_request`

... bring it into line with CAS and OIDC by making it take a Request parameter,
move the magic for `client_redirect_url` for UIA into the handler, and fix the
return type to be a `str` rather than a `bytes`.

* Define a common protocol for SSO auth provider impls

* Give SsoIdentityProvider an ID and register them

* Combine the SSO Redirect servlets

Now that the SsoHandler knows about the identity providers, we can combine the
various *RedirectServlets into a single implementation which delegates to the
right IdP.

* changelog

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/9015.feature b/changelog.d/9015.feature
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index 0000000000..01a24dcf49
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+++ b/changelog.d/9015.feature
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+Add support for multiple SSO Identity Providers.