Signing in with uppercase username breaks device list updates

[matrixbot]

This issue was originally created by @nico-famedly at https://github.com/matrix-org/dendrite/issues/2914.

Background information

• Dendrite version or git SHA: 0.10.8+ed497aa
• Monolith or Polylith?: Monolith
• SQLite3 or Postgres?: sqlite
• Running in Docker?: yes
• go version:
• Client used (if applicable): famedlysdk, but shouldn't matter

Description

• What is the problem: If I sign in using Bob instead of bob, I get a device list update for @Bob:localhost instead of @bob:localhost with only one entry
• Who is affected: Uhhh, everyone who uses an uppercase username to sign in?
• How is this bug manifesting: Wrong device lists, that break e2ee
• When did this first appear:

Steps to reproduce

• curl -fS -XPOST -d '{"username":"bob", "password":"Something", "inhibit_login":true, "auth": {"type":"m.login.dummy"}}' "http://$IP_ADDRESS/_matrix/client/r0/register"
• then login using Bob as the identifier for the user
• login succeeds
• If you share an encrypted room with bob, you will get a device list update for @Bob:servername instead of @bob:servername

I would expect device lists to always use the exact mxid instead of the casing from /login.

Logs:

# Normal login using "bob"

Updating device keys for {@bob:famedlysdk.test: []}

Response {@bob:famedlysdk.test: {pnv71Ijt: Instance of 'MatrixDeviceKeys'}}

# Login using "Bob"

[Matrix] Successfully connected as Bob with http://127.0.0.1

Updating device keys for {@Bob:famedlysdk.test: []}

Response {@Bob:famedlysdk.test: {2Cfqnc6M: Instance of 'MatrixDeviceKeys'}}

Notice how the latter does not include the devices form "bob" and uses the wrong mxid in the response.

[matrixbot]

This comment was originally posted by @bones-was-here at https://github.com/matrix-org/dendrite/issues/2914#issuecomment-1352408749.

How are you able to log in with an uppercase char?

I still patch the source to support very old accounts https://github.com/matrix-org/dendrite/issues/2073#issuecomment-1047934258

[matrixbot]

This comment was originally posted by @deepbluev7 at https://github.com/matrix-org/dendrite/issues/2914#issuecomment-1360685157.

@bones-was-here I just passed "Bob" as the login username and it worked. The actual useraccount in the database is lower case, since it is lowercased on registration and login, but the signed in user is treated as if the localpart was uppercase.