diff --git a/lib/SimpleSAML/Auth/ProcessingChain.php b/lib/SimpleSAML/Auth/ProcessingChain.php
index b034220d9204cf5662a8d962505a087c8edaabf1..fdf1ba96a944ad3d0bf0ded46c530803e7d26423 100644
--- a/lib/SimpleSAML/Auth/ProcessingChain.php
+++ b/lib/SimpleSAML/Auth/ProcessingChain.php
@@ -184,6 +184,7 @@ class SimpleSAML_Auth_ProcessingChain {
 
 		try {
 
+			// TODO: remove this in SSP 2.0
 			if (!array_key_exists('UserID', $state)) {
 				/* No unique user ID present. Attempt to add one. */
 				self::addUserID($state);
@@ -283,6 +284,7 @@ class SimpleSAML_Auth_ProcessingChain {
 
 		$state[self::FILTERS_INDEX] = $this->filters;
 
+		// TODO: remove this in SSP 2.0
 		if (!array_key_exists('UserID', $state)) {
 			/* No unique user ID present. Attempt to add one. */
 			self::addUserID($state);
@@ -313,11 +315,7 @@ class SimpleSAML_Auth_ProcessingChain {
 
 
 	/**
-	 * Add unique user ID.
-	 *
-	 * This function attempts to add an unique user ID to the state.
-	 *
-	 * @param array &$state  The state we should update.
+	 * @deprecated This method will be removed in SSP 2.0.
 	 */
 	private static function addUserID(&$state) {
 		assert('is_array($state)');
@@ -325,8 +323,10 @@ class SimpleSAML_Auth_ProcessingChain {
 
 		if (isset($state['Destination']['userid.attribute'])) {
 			$attributeName = $state['Destination']['userid.attribute'];
+			SimpleSAML_Logger::warning("The 'userid.attribute' option has been deprecated.");
 		} elseif (isset($state['Source']['userid.attribute'])) {
 			$attributeName = $state['Source']['userid.attribute'];
+			SimpleSAML_Logger::warning("The 'userid.attribute' option has been deprecated.");
 		} else {
 			/* Default attribute. */
 			$attributeName = 'eduPersonPrincipalName';