diff --git a/lib/AutodiscoverMicrosoft.php b/lib/AutodiscoverMicrosoft.php
--- a/lib/AutodiscoverMicrosoft.php
+++ b/lib/AutodiscoverMicrosoft.php
@@ -42,13 +42,6 @@
     {
         $post = $_SERVER['REQUEST_METHOD'] == 'POST' ? file_get_contents('php://input') : null;
 
-        // check for basic authentication
-        Log::debug('Request [microsoft]: Basic Auth Username: ' . ($_SERVER['PHP_AUTH_USER'] ?: 'none'));
-        if (empty($_SERVER['PHP_AUTH_USER']) || empty($_SERVER['PHP_AUTH_PW'])) {
-            $this->unauthorized();
-        }
-        $this->password = $_SERVER['PHP_AUTH_PW'];
-
         // check for request object
         Log::debug('Request [microsoft]: ' . $post);
         if (empty($post)) {
@@ -82,9 +75,19 @@
             $this->error("Invalid input");
         }
 
-        // basic auth username must match with given email address
-        if ($_SERVER['PHP_AUTH_USER'] != $this->email) {
-            $this->unauthorized();
+        // check for basic authentication if ldap is available
+        if (!empty($this->_ldap_server)) {
+            Log::debug('Request [microsoft]: Basic Auth Username: ' . ($_SERVER['PHP_AUTH_USER'] ?: 'none'));
+            if (empty($_SERVER['PHP_AUTH_USER']) || empty($_SERVER['PHP_AUTH_PW'])) {
+                $this->unauthorized();
+            }
+
+            // basic auth username must match with given email address
+            if ($_SERVER['PHP_AUTH_USER'] != $this->email) {
+                $this->unauthorized();
+            }
+
+            $this->password = $_SERVER['PHP_AUTH_PW'];
         }
     }
 
@@ -93,9 +96,11 @@
      */
     public function handle_response()
     {
-        // authenticate the user found during configure() against ldap
-        if (empty($this->config['dn']) || !$this->authenticate($this->config['dn'], $this->password)) {
-            $this->unauthorized();
+        if (!empty($this->_ldap_server)) {
+            // authenticate the user found during configure() against ldap
+            if (empty($this->config['dn']) || !$this->authenticate($this->config['dn'], $this->password)) {
+                $this->unauthorized();
+            }
         }
 
         $method = $this->type . '_response';