[Web][Dovecot] Do not count logins as failed while the identity provider is unavailable

data/conf/dovecot/auth/mailcowauth.php

@@ -101,7 +101,16 @@ if ($result === false){
   // Init Identity Provider
   $iam_provider = identity_provider('init');
   $iam_settings = identity_provider('get');
-  $result = user_login($post['username'], $post['password'], array('is_internal' => true, 'service' => $post['service']));
+  try {
+    $result = user_login($post['username'], $post['password'], array('is_internal' => true, 'service' => $post['service']));
+  } catch (\Mailcow\Auth\IdpUnavailable $e) {
+    // temporary failure for Dovecot, no failed login
+    error_log("MAILCOWAUTH: Identity provider unavailable for user " . $post['username'] . " with service " . $post['service'] . " from IP " . $post['real_rip'] . ": " . $e->getMessage());
+    http_response_code(503); // Service Unavailable
+    echo json_encode($return);
+    session_destroy();
+    exit;
+  }
   if ($result) {
     error_log('MAILCOWAUTH: User auth for user ' . $post['username'] . " with service " . $post['service'] . " from IP " . $post['real_rip']);
     set_sasl_log($post['username'], $post['real_rip'], $post['service']);

data/conf/dovecot/auth/passwd-verify.lua

@@ -41,6 +41,12 @@ function auth_password_verify(request, password)
     return dovecot.auth.PASSDB_RESULT_INTERNAL_FAILURE, "Upstream unreachable"
   end
 
+  -- 5xx: the backend or the identity provider cannot answer, a temporary failure and no failed login
+  if c >= 500 then
+    dovecot.i_info("HTTP request to auth backend failed with " .. tostring(c) .. " for user " .. request.user)
+    return dovecot.auth.PASSDB_RESULT_INTERNAL_FAILURE, "Upstream unavailable"
+  end
+
   if c ~= 200 and c ~= 401 then
     dovecot.i_info("HTTP request failed with " .. tostring(c) .. " for user " .. request.user)
     return dovecot.auth.PASSDB_RESULT_PASSWORD_MISMATCH, "Upstream error"

data/conf/dovecot/dovecot.conf

@@ -67,9 +67,11 @@ passdb {
 }
 # check for regular password - if empty (e.g. force-passwd-reset), previous pass=yes passdbs also fail
 # a return of the following passdb is mandatory
+# cache_key with password: the lua default (%u) would let a temporary failure fall back to the negative entry
+# of a passdb lookup (master logins) and log "unknown user", which netfilter counts as failed login
 passdb {
   driver = lua
-  args = file=/etc/dovecot/auth/passwd-verify.lua blocking=yes
+  args = file=/etc/dovecot/auth/passwd-verify.lua blocking=yes cache_key=%s:%u:%w
 }
 # Set doveadm_password=your-secret-password in data/conf/dovecot/extra.conf (create if missing)
 service doveadm {