Add trace logging to SSO methods (#15803)

It is currenly impossible to detect which "SSO" method is responsible for login. This
PR adds some basic trace logging to these methods.

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/auth/sso/reverseproxy.go

@@ -65,6 +65,7 @@ func (r *ReverseProxy) VerifyAuthData(req *http.Request, w http.ResponseWriter,
 	if len(username) == 0 {
 		return nil
 	}
+	log.Trace("ReverseProxy Authorization: Found username: %s", username)
 
 	user, err := models.GetUserByName(username)
 	if err != nil {
@@ -75,6 +76,7 @@ func (r *ReverseProxy) VerifyAuthData(req *http.Request, w http.ResponseWriter,
 		return nil
 	}
 
+	log.Trace("ReverseProxy Authorization: Logged in user %-v", user)
 	return user
 }