1721-rename-cas-to-sso.md

MSC1721: Rename m.login.cas to m.login.sso

The Matrix Client-Server spec includes a section on client login using Central Authentication Service (CAS).

The spec currently fails to mention it, but this process is triggered when GET /login returns a flow type of m.login.cas.

Nothing in this flow is specific to CAS - it is equally applicable for other web-based single-sign-on processes, such as SAML.

Accordingly, we should rename cas to sso.

Proposal

1. m.login.sso should be defined as a valid login type for return from GET /login. (We should probably mention m.login.cas in the spec while we are there.)

2. When a client wishes to use the SSO login type, it should redirect to /_matrix/client/r0/login/sso/redirect (instead of /_matrix/client/r0/login/cas/redirect).

3. Servers should treat /_matrix/client/r0/login/sso/redirect identically to /_matrix/client/r0/login/cas/redirect: they should issue a redirect to their configured single-sign-on system.

4. Servers which support m.login.sso should make sure they update their login fallback page to understand the new login type.