* 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
The final part (for now) of my work to implement a username picker in synapse itself. The idea is that we allow
`UsernameMappingProvider`s to return `localpart=None`, in which case, rather than redirecting the browser
back to the client, we redirect to a username-picker resource, which allows the user to enter a username.
We *then* complete the SSO flow (including doing the client permission checks).
The static resources for the username picker itself (in
https://github.com/matrix-org/synapse/tree/rav/username_picker/synapse/res/username_picker)
are essentially lifted wholesale from
https://github.com/matrix-org/matrix-synapse-saml-mozilla/tree/master/matrix_synapse_saml_mozilla/res.
As the comment says, we might want to think about making them customisable, but that can be a follow-up.
Fixes#8876.
This is another part of my work towards fixing #8876. It moves some of the logic currently in the SAML and OIDC handlers - in particular the call to `AuthHandler.complete_sso_login` down into the `SsoHandler`.
* Factor out _call_attribute_mapper and _register_mapped_user
This is mostly an attempt to simplify `get_mxid_from_sso`.
* Move mapping_lock down into SsoHandler.
* SsoHandler: remove inheritance from BaseHandler
* Simplify the flow for SSO UIA
We don't need to do all the magic for mapping users when we are doing UIA, so
let's factor that out.
This was broken in #8801 when abstracting code shared with OIDC.
After this change both SAML and OIDC have a concept of
grandfathering users, but with different implementations.
