discourse/discourse — pull request #2080 by Xenograph (2014-03-08 06:18:40+00:00)
Title:  Username/email change should not be allowed with SSO and username/email override enabled

If both SiteSetting.enable_sso and SiteSetting.sso_overrides_username are enabled, username changing should be disabled globally, since that combination of settings would suggest that the external SSO database is fully authoritative with respect to usernames. Likewise, the same should apply for emails.