Support for mandatory backup/passphrase from .well-known configuration

[jmartinesp]

Your use case

What would you like to do?

Home Servers admins can enable mandatory backup in /.well-known/matrix/client by returning:

"io.element.e2ee": {
  "secure_backup_required": true
  "secure_backup_setup_methods": ["passphrase"] (optional, defaults to "all methods accepted")
}

The client should make secure key/passphrase backup & session verification mandatory on login/account creation if this option is enabled.

Have you considered any alternatives?

No response

Additional context

No response