Correction of redirect URL after successful SAML login

From my perspective, if agreed, this change can be merged, because the basic SAM auth. functionality is now present
and was tested with "samlidp.io" iDP.

However, there are further improvements which I would like to integrate, but as a separate features in separate pull requests

powerdnsadmin/routes/index.py

@@ -663,7 +663,7 @@ def saml_authorized():
         user.update_profile()
         session['authentication_type'] = 'SAML'
         login_user(user, remember=False)
-        return redirect(url_for('index'))
+        return redirect(url_for('index.login'))
     else:
         return render_template('errors/SAML.html', errors=errors)