crypto: Use the server name in the QR code login data

[poljar]

Using the resolved homeserver URL causes problems if we need to inspect the well-known configuration of the homeserver, for example, if the server name is matrix.org, but the homeserver URL is server.matrix.org, the well-known might be only available for the former.

This is why we also need to receive the former, i.e. the server name in the QR code data.

• Public API changes documented in changelogs (optional)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.79%. Comparing base (abda959) to head (cd51c40).
Report is 26 commits behind head on main.

Additional details and impacted files

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##             main    #3537   +/-   ##
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  Coverage   83.79%   83.79%           
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  Files         254      254           
  Lines       25734    25734           
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  Hits        21563    21563           
  Misses       4171     4171           

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[bnjbvr]

Mostly nits, so approving. The code makes sense, I'm not too sure about the why of the change, but trust you here. (Alternatively, one could ask review from somebody who's more knowledgeable about the QR code login process.)

[poljar]

Mostly nits, so approving. The code makes sense, I'm not too sure about the why of the change, but trust you here. (Alternatively, one could ask review from somebody who's more knowledgeable about the QR code login process.)

The MSC got changed: matrix-org/matrix-spec-proposals@87f8317. The commit attempts to clarify why as well, you need to be able to do the well-known discovery, which is guaranteed to only work if you get the server name.