Login: Implement Token-based authentication

[anoadragon453]

Spec URL: https://matrix.org/docs/spec/client_server/r0.3.0.html#post-matrix-client-r0-login https://matrix.org/docs/spec/client_server/r0.5.0#token-based

Difficulty: Medium

https://github.com/matrix-org/dendrite/blob/dfcf31f293a319830e2b8a188413db776930a5e5/src/github.com/matrix-org/dendrite/clientapi/routing/login.go#L60-L146

We currently only allow password-based authentication for login. Token-based authentication will be necessary for basic operation with clients. Currently users have tokens generated for them, we just need to check them on login.

Summary:

• [ ] Differentiate between "type": "m.login.token" and "m.login.password" in request body
• [ ] Authenticate user based on token and device ID. Relationship between access tokens and devices
• [ ] Create test case(s) for logging in with access token

[APwhitehat]

@anoadragon453 This is phase 1 as well, may I take this up ?

[anoadragon453]

@APwhitehat Certainly!

[tommie]

I'm forking #1374 and splitting apart the login stuff to be PRd separately first.