support other forms of login other than password, depending on config options

[fabius]

One should be able to configure which forms of authentication are enabled on a dendrite instance. As stated here https://github.com/matrix-org/dendrite/blob/3b7a4ad640f260b3918a35684b05ced077a09f0c/clientapi/routing/login.go#L62

I'd be happy to work on this unless some work is already in progress. This is somewhat related to the portable identities proposal because it requires a different auth mechanism.

[kegsay]

Dupe of issues which specify the other forms:

• JWTS #1626
• Email #1298
• SSO #1297
• Tokens #403

[compgeniuses]

Dupe of issues which specify the other forms:

• JWTS JWT login  #1626
• Email Implement registering with an email support #1298
• SSO Implement SSO for logins #1297
• Tokens Login: Implement Token-based authentication #403

IF this issue is Closed, shouldnt all other list of issues that specify other form be also closed, for the sake of closure.

Otherwise youll have many open issues, yet most are done, and someone who really wants to work on an issue will be frstated, every time going through an issue thats open its done, but not closed

Just my thoughts.