Auth: Log a more useful msg if no OAuth provider configured (#56722)

Log a useful msg if no oauth provider configured

When a user doesn't configure an OAuth provider and uses auto login, Grafana logs a misleading message indicating that he has multiple providers configured.

pkg/api/login.go

@@ -142,9 +142,12 @@ func (hs *HTTPServer) tryOAuthAutoLogin(c *models.ReqContext) bool {
 		return false
 	}
 	oauthInfos := hs.SocialService.GetOAuthInfoProviders()
-	if len(oauthInfos) != 1 {
+	if len(oauthInfos) > 1 {
 		c.Logger.Warn("Skipping OAuth auto login because multiple OAuth providers are configured")
 		return false
+	} else if len(oauthInfos) == 0 {
+		c.Logger.Warn("Skipping OAuth auto login because no OAuth providers are configured")
+		return false
 	}
 	for key := range oauthInfos {
 		redirectUrl := hs.Cfg.AppSubURL + "/login/" + key