Well-known lookup for homeserver url

If my Synapse is hosted at https://matrix.example.com but my Synapse server name is https://example.com, typing https://example.com into the server URL should do a well-known lookup as per hhttps://matrix.org/docs/spec/client_server/r0.6.0#server-discovery

Related to but separate from #476

[aaronraimist]

Yeah. The comment I made in #riotx:matrix.org before I went searching for issues was

Is the current login flow pretty early still or is this close to the final design?

I think the login flow should emphasize entering your full username and having the .well-known lookup done rather than entering the homeserver URL which should be a more advanced/last resort feature.

https://github.com/vector-im/riotX-android/issues/476 is what the login screen should do, with like a tiny little option at the bottom to enter the homeserver URL for the one homeserver out there that doesn’t have .well-known.

Since the spec says you can’t do a well-known lookup on an explicitly entered homeserver URL we should be training users to always enter their full MXID and then they never need to know anything about the homeserver URL.

[aaronraimist]

RiotX has implemented this now even though other Riots have not done so. A decision needs to be made so all clients implement it in the same way, otherwise it is confusing for users.