Refactor O365 login to use server-side state and add account support

Co-authored-by: kristofer.john.nilsson <kristofer.john.nilsson@gmail.com>

plugins/login-o365/LoginOAuth2.js

@@ -1,38 +1,37 @@
 ((rl) => {
   const client_id = rl.pluginSettingsGet("login-o365", "client_id"),
-    // https://learn.microsoft.com/en-us/entra/identity-platform/reply-url#query-parameter-support-in-redirect-uris
-    tenant = rl.pluginSettingsGet("login-o365", "tenant"),
-    login = () => {
-      document.location = "https://login.microsoftonline.com/" +
-        tenant +
-        "/oauth2/v2.0/authorize?" +
-        new URLSearchParams({
-          response_type: "code",
-          client_id: client_id,
-          redirect_uri:
-            document.location.href.replace(/\/$/, "") + "/LoginO365",
-          scope: [
-            // Associate personal info
-            "openid",
-            "offline_access",
-            "email",
-            "profile",
-            // Access IMAP and SMTP through OAUTH
-            "https://outlook.office.com/IMAP.AccessAsUser.All",
-            "https://outlook.office.com/SMTP.Send",
-          ].join(" "),
-          state: "o365",
-          access_type: "offline_access"
-          // prompt: "consent",
-        });
+    allowAnyDomain = !!rl.pluginSettingsGet("login-o365", "allow_any_domain"),
+    isSupportedEmail = (email) => {
+      email = (email || "").toLowerCase();
+      if (!email.includes("@")) return false;
+      if (allowAnyDomain) return true;
+      return /@(outlook\.com|hotmail\.com|live\.com)$/.test(email);
+    },
+    startOAuth = (op, opts = {}) => {
+      const email = (opts.email || "").toLowerCase();
+      const name = opts.name || "";
+      const returnHash = opts.return || "";
+
+      // Server mints a signed state + correct redirect_uri and returns full authUrl.
+      rl.pluginRemoteRequest((iError, data) => {
+        const url = data?.Result?.authUrl;
+        if (!iError && url) {
+          document.location = url;
+        }
+      }, "LoginO365AuthUrl", {
+        op: op,
+        email: email,
+        name: name,
+        return: returnHash,
+      });
     };
 
   if (client_id) {
     addEventListener("sm-user-login", (e) => {
       const email = (e.detail.get("Email") || "").toLowerCase();
-      if (/@(outlook\.com|hotmail\.com|live\.com)$/.test(email)) {
+      if (isSupportedEmail(email)) {
         e.preventDefault();
-        login();
+        startOAuth("login", { email });
       }
     });
 
@@ -42,10 +41,51 @@
 		  container = e.detail.viewModelDom.querySelector("#plugin-Login-BottomControlGroup"),
           btn = Element.fromHTML('<button type="button">Outlook</button>'),
           div = Element.fromHTML('<div class="controls"></div>');
-        btn.onclick = login;
+        btn.onclick = () => {
+          // Best-effort: try to read the email field if present.
+          const input = e.detail.viewModelDom.querySelector('input[type="email"], input[name="Email"], input[name="email"], input');
+          const email = (input?.value || "").toLowerCase();
+          if (!email || isSupportedEmail(email)) {
+            startOAuth("login", { email });
+          }
+        };
         div.append(btn);
         container && container.append(div);
       }
+
+      // "Add account" popup (Settings → Accounts → Add account)
+      if ("Account" === e.detail.viewModelTemplateID) {
+        // Only for the "Add account" mode, not "Edit account".
+        if (typeof e.detail.isNew === "function" && !e.detail.isNew()) {
+          return;
+        }
+        const root = e.detail.viewModelDom;
+        if (!root) return;
+
+        const footer = root.querySelector("footer");
+        const form = root.querySelector("#accountform");
+        const addButton = root.querySelector("button.buttonAddAccount");
+        if (!footer || !form || !addButton) return;
+
+        // Avoid inserting duplicates when view model is re-rendered.
+        if (root.querySelector(".plugin-o365-add-account")) return;
+
+        const btn = Element.fromHTML(
+          '<button type="button" class="btn plugin-o365-add-account" style="margin-left: 6px;">Outlook</button>'
+        );
+
+        btn.onclick = () => {
+          const email = (form.querySelector('input[name="email"]')?.value || "").trim().toLowerCase();
+          const name = (form.querySelector('input[name="name"]')?.value || "").trim();
+          if (!email || !isSupportedEmail(email)) {
+            return;
+          }
+          startOAuth("add", { email, name, return: document.location.hash || "#/settings/accounts" });
+        };
+
+        // Put the button next to the default Add Account submit button.
+        footer.insertBefore(btn, addButton.nextSibling);
+      }
     });
   }
 })(window.rl);

plugins/login-o365/index.php

@@ -7,8 +7,8 @@
  *     https://outlook.office.com/SMTP.Send
  *     openid offline_access email profile
  * https://learn.microsoft.com/en-us/entra/identity-platform/reply-url#query-parameter-support-in-redirect-uris
- * Azure:    redirect_uri=https://{DOMAIN}/?LoginO365
- * Personal: redirect_uri=https://{DOMAIN}/LoginO365
+ * Query: redirect_uri=https://{DOMAIN}/?LoginO365
+ * Path:  redirect_uri=https://{DOMAIN}/LoginO365
  * 
  * If running behind nginx reverse proxy you might
  * need to add the following to your nginx config:
@@ -24,8 +24,8 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
 {
     const
         NAME     = 'Office365/Outlook OAuth2',
-        VERSION  = '0.3',
-        RELEASE  = '2025-12-18',
+        VERSION  = '0.4',
+        RELEASE  = '2025-12-22',
         REQUIRED = '2.36.1',
         CATEGORY = 'Login',
         DESCRIPTION = 'Office365/Outlook IMAP, Sieve & SMTP login using RFC 7628 OAuth2';
@@ -35,7 +35,17 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
         AUTH_URI  = 'https://login.microsoftonline.com/{{tenant}}/oauth2/v2.0/authorize',
         TOKEN_URI = 'https://login.microsoftonline.com/{{tenant}}/oauth2/v2.0/token';
 
-    private static ?array $auth = null;
+    /**
+     * In-request cache of decrypted token bundles, keyed by lowercase email.
+     * This avoids re-decrypting the same blob multiple times during a single request.
+     *
+     * Shape:
+     *   [
+     *     'user@outlook.com' => ['access_token'=>..., 'refresh_token'=>..., 'expires'=>..., 'expires_in'=>...],
+     *     ...
+     *   ]
+     */
+    private static array $auth = [];
 
     public function Init() : void
     {
@@ -46,9 +56,14 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
         $this->addHook('sieve.before-login', 'clientLogin');
 
         $this->addPartHook('LoginO365', 'ServiceLoginO365');
+        // Used by JS to obtain an auth URL with signed state (for both login + add-account flows).
+        $this->addJsonHook('LoginO365AuthUrl', 'DoLoginO365AuthUrl');
 
         // Prevent Disallowed Sec-Fetch Dest: document Mode: navigate Site: cross-site User: true
         $this->addHook('filter.http-paths', 'httpPaths');
+
+        // Cleanup: when an additional account is removed, also remove its encrypted refresh token bundle.
+        $this->addHook('json.after-AccountDelete', 'afterAccountDelete');
     }
 
     public function httpPaths(array &$aPaths) : void
@@ -79,7 +94,7 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
             }
 
             // Must have code + state
-            if (!isset($_GET['code']) || empty($_GET['state']) || 'o365' !== $_GET['state']) {
+            if (!isset($_GET['code']) || empty($_GET['state'])) {
                 $oActions->Location(\RainLoop\Utils::WebPath());
                 exit;
             }
@@ -92,23 +107,17 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
 
             $iNow = \time();
 
-            // Build absolute base URL (works behind nginx reverse proxy)
-            $scheme = (!empty($_SERVER['HTTP_X_FORWARDED_PROTO']))
-                ? $_SERVER['HTTP_X_FORWARDED_PROTO']
-                : ((!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off') ? 'https' : 'http');
-
-            $host = $_SERVER['HTTP_HOST'] ?? $_SERVER['SERVER_NAME'] ?? '';
-            if (!$host) {
-                throw new \RuntimeException('Cannot determine HTTP_HOST');
-            }
-            $base = $scheme . '://' . $host;
-
-            // IMPORTANT: default personal=false to match the JS default behavior
-            $personal = (bool)$this->Config()->Get('plugin', 'personal', false);
-            $redirectUri = $personal ? ($base . '/?LoginO365') : ($base . '/LoginO365');
+            $redirectUri = $this->redirectUri();
 
             $tenant = $this->Config()->Get('plugin', 'tenant', 'common');
 
+            $state = (string) $_GET['state'];
+            $statePayload = $this->verifyAndConsumeState($state);
+            if (!$statePayload) {
+                $oActions->Location(\RainLoop\Utils::WebPath());
+                exit;
+            }
+
             $aTokenWrap = $oO365->getAccessToken(
                 \str_replace('{{tenant}}', $tenant, static::TOKEN_URI),
                 'authorization_code',
@@ -161,13 +170,69 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
                 throw new \RuntimeException('unknown email address from id_token');
             }
 
-            static::$auth = [
+            if (!$this->isSupportedEmail(\strtolower($email))) {
+                throw new \RuntimeException('Unsupported email domain for this plugin');
+            }
+
+            $tokenBundle = [
                 'access_token' => $accessToken,
                 'refresh_token' => $refreshToken,
                 'expires_in' => $expiresIn,
                 'expires' => $iNow + $expiresIn
             ];
 
+            $op = $statePayload['op'] ?? 'login';
+            if ('add' === $op) {
+                $oMainAccount = $oActions->getMainAccountFromToken(false);
+                if (!$oMainAccount) {
+                    throw new \RuntimeException('Add-account flow requires logged in main account');
+                }
+                if (!empty($statePayload['main']) && $statePayload['main'] !== $oMainAccount->Email()) {
+                    throw new \RuntimeException('Add-account state does not match current main account');
+                }
+
+                // Store token bundle encrypted with MAIN account crypt key (never store refresh_token unencrypted).
+                // This is later used by imap/smtp/sieve.before-login for *additional* accounts.
+                $this->storeAccountTokens($oMainAccount, $email, $tokenBundle);
+
+                // Create/validate an AdditionalAccount entry exactly like SnappyMail expects in "additionalaccounts".
+                // We set the "password" to the OAuth subject (sub) as an opaque secret; the plugin will inject XOAUTH2.
+                $oPassword = new \SnappyMail\SensitiveString($sub);
+                $oAdditional = $oActions->LoginProcess($email, $oPassword, false);
+                if (!$oAdditional instanceof \RainLoop\Model\AdditionalAccount) {
+                    throw new \RuntimeException('Failed to create additional account');
+                }
+
+                $asciiEmail = \SnappyMail\IDN::emailToAscii($oAdditional->Email());
+                if ($asciiEmail === $oMainAccount->Email()) {
+                    throw new \RuntimeException('Cannot add main account as additional');
+                }
+
+                $aAccounts = $oActions->GetAccounts($oMainAccount);
+                $aEntry = $oAdditional->asTokenArray($oMainAccount);
+                if (!empty($statePayload['name']) && \is_string($statePayload['name'])) {
+                    $aEntry['name'] = \trim($statePayload['name']);
+                } else if (isset($aAccounts[$asciiEmail]['name'])) {
+                    // Preserve previous custom label if re-adding/updating.
+                    $aEntry['name'] = (string) $aAccounts[$asciiEmail]['name'];
+                }
+                $aAccounts[$asciiEmail] = $aEntry;
+                $oActions->SetAccounts($oMainAccount, $aAccounts);
+
+                // Cache for this request (used during LoginProcess() above and any subsequent logins).
+                static::$auth[\strtolower($asciiEmail)] = $tokenBundle;
+
+                $returnHash = '';
+                if (!empty($statePayload['return']) && \is_string($statePayload['return']) && \str_starts_with($statePayload['return'], '#')) {
+                    $returnHash = $statePayload['return'];
+                }
+                $oActions->Location(\RainLoop\Utils::WebPath() . $returnHash);
+                exit;
+            }
+
+            // Default: "login" flow (preserve existing behavior)
+            static::$auth[\strtolower($email)] = $tokenBundle;
+
             // SnappyMail uses password as opaque string; plugin injects XOAUTH2 later.
             $oPassword = new \SnappyMail\SensitiveString($sub);
             $oAccount = $oActions->LoginProcess($email, $oPassword);
@@ -177,7 +242,7 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
                     $oAccount,
                     StorageType::SESSION,
                     \RainLoop\Utils::GetSessionToken(),
-                    \SnappyMail\Crypt::EncryptToJSON(static::$auth, $oAccount->CryptKey())
+                    \SnappyMail\Crypt::EncryptToJSON($tokenBundle, $oAccount->CryptKey())
                 );
             }
         }
@@ -206,7 +271,14 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
                 ->SetDefaultValue(['common','consumers','organizations'])
                 ->SetAllowedInJs(),
             \RainLoop\Plugins\Property::NewInstance('personal')
-                ->SetLabel('Use /LoginO365 redirect path')
+                // When true: redirect URI uses query parameter form "/?LoginO365" (Azure supports it).
+                // When false: redirect URI uses path form "/LoginO365" (useful behind reverse proxies).
+                ->SetLabel('Use "/?LoginO365" redirect URI')
+                ->SetType(\RainLoop\Enumerations\PluginPropertyType::BOOL)
+                ->SetDefaultValue(false)
+                ->SetAllowedInJs(),
+            \RainLoop\Plugins\Property::NewInstance('allow_any_domain')
+                ->SetLabel('Allow any domain (not only outlook.com/hotmail.com/live.com)')
                 ->SetType(\RainLoop\Enumerations\PluginPropertyType::BOOL)
                 ->SetDefaultValue(false)
                 ->SetAllowedInJs()
@@ -217,69 +289,115 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
     {
         $email = \strtolower($oAccount->Email());
 
-        if (
-            $oAccount instanceof MainAccount
-            && (
-                \str_ends_with($email, '@hotmail.com')
-                || \str_ends_with($email, '@outlook.com')
-                || \str_ends_with($email, '@live.com')
-            )
-        ) {
-            $oActions = \RainLoop\Api::Actions();
+        if (!$this->isSupportedEmail($email)) {
+            return;
+        }
 
+        $oActions = \RainLoop\Api::Actions();
+
+        $aData = static::$auth[$email] ?? null;
+        if (!$aData) {
             try {
-                $blob = $oActions->StorageProvider()->Get(
-                    $oAccount,
-                    StorageType::SESSION,
-                    \RainLoop\Utils::GetSessionToken()
-                );
-
-                $aData = static::$auth ?: \SnappyMail\Crypt::DecryptFromJSON($blob, $oAccount->CryptKey());
+                if ($oAccount instanceof MainAccount) {
+                    $blob = $oActions->StorageProvider()->Get(
+                        $oAccount,
+                        StorageType::SESSION,
+                        \RainLoop\Utils::GetSessionToken()
+                    );
+                    $aData = \SnappyMail\Crypt::DecryptFromJSON($blob, $oAccount->CryptKey());
+                } else if ($oAccount instanceof \RainLoop\Model\AdditionalAccount) {
+                    $oMain = $oActions->getMainAccountFromToken(false);
+                    if (!$oMain) {
+                        return;
+                    }
+                    $blob = $oActions->StorageProvider()->Get(
+                        $oMain,
+                        StorageType::CONFIG,
+                        $this->tokenStorageKey($email)
+                    );
+                    $aData = \SnappyMail\Crypt::DecryptFromJSON($blob, $oMain->CryptKey());
+                }
             } catch (\Throwable $e) {
                 return;
             }
+        }
 
-            if (empty($aData['access_token']) || empty($aData['refresh_token']) || empty($aData['expires'])) {
-                return;
-            }
+        if (empty($aData['access_token']) || empty($aData['refresh_token']) || empty($aData['expires'])) {
+            return;
+        }
 
-            // Refresh if expired
-            if (\time() >= (int)$aData['expires']) {
-                $oO365 = $this->o365Connector();
-                if ($oO365) {
-                    $tenant = $this->Config()->Get('plugin', 'tenant', 'common');
-                    $aRefreshWrap = $oO365->getAccessToken(
-                        \str_replace('{{tenant}}', $tenant, static::TOKEN_URI),
-                        'refresh_token',
-                        ['refresh_token' => $aData['refresh_token']]
-                    );
+        // Refresh if expired (or close to expiry)
+        if (\time() >= ((int)$aData['expires'] - 30)) {
+            $oO365 = $this->o365Connector();
+            if ($oO365) {
+                $tenant = $this->Config()->Get('plugin', 'tenant', 'common');
+                $aRefreshWrap = $oO365->getAccessToken(
+                    \str_replace('{{tenant}}', $tenant, static::TOKEN_URI),
+                    'refresh_token',
+                    ['refresh_token' => $aData['refresh_token']]
+                );
 
-                    if (\is_array($aRefreshWrap) && isset($aRefreshWrap['code']) && 200 === (int)$aRefreshWrap['code']) {
-                        $r = $aRefreshWrap['result'] ?? [];
-                        if (!empty($r['access_token'])) {
-                            $aData['access_token'] = $r['access_token'];
-                        }
-                        if (!empty($r['refresh_token'])) {
-                            $aData['refresh_token'] = $r['refresh_token'];
-                        }
-                        $expiresIn = (int)($r['expires_in'] ?? 0);
-                        if ($expiresIn > 0) {
-                            $aData['expires'] = \time() + $expiresIn;
-                        }
+                if (\is_array($aRefreshWrap) && isset($aRefreshWrap['code']) && 200 === (int)$aRefreshWrap['code']) {
+                    $r = $aRefreshWrap['result'] ?? [];
+                    if (!empty($r['access_token'])) {
+                        $aData['access_token'] = $r['access_token'];
+                    }
+                    if (!empty($r['refresh_token'])) {
+                        $aData['refresh_token'] = $r['refresh_token'];
+                    }
+                    $expiresIn = (int)($r['expires_in'] ?? 0);
+                    if ($expiresIn > 0) {
+                        $aData['expires'] = \time() + $expiresIn;
+                        $aData['expires_in'] = $expiresIn;
+                    }
 
+                    // Persist updated bundle (encrypted).
+                    if ($oAccount instanceof MainAccount) {
                         $oActions->StorageProvider()->Put(
                             $oAccount,
                             StorageType::SESSION,
                             \RainLoop\Utils::GetSessionToken(),
                             \SnappyMail\Crypt::EncryptToJSON($aData, $oAccount->CryptKey())
                         );
+                    } else if ($oAccount instanceof \RainLoop\Model\AdditionalAccount) {
+                        $oMain = $oActions->getMainAccountFromToken(false);
+                        if ($oMain) {
+                            $oActions->StorageProvider()->Put(
+                                $oMain,
+                                StorageType::CONFIG,
+                                $this->tokenStorageKey($email),
+                                \SnappyMail\Crypt::EncryptToJSON($aData, $oMain->CryptKey())
+                            );
+                        }
                     }
                 }
             }
+        }
 
-            // Inject XOAUTH2/OAUTHBEARER
-            $oSettings->passphrase = $aData['access_token'];
-            \array_unshift($oSettings->SASLMechanisms, 'OAUTHBEARER', 'XOAUTH2');
+        static::$auth[$email] = $aData;
+
+        // Inject XOAUTH2/OAUTHBEARER
+        $oSettings->passphrase = $aData['access_token'];
+        \array_unshift($oSettings->SASLMechanisms, 'OAUTHBEARER', 'XOAUTH2');
+    }
+
+    /**
+     * Server-side cleanup hook: after a successful AccountDelete, remove stored token bundle for that email.
+     * This prevents leaving encrypted refresh tokens behind when an additional account is removed.
+     */
+    public function afterAccountDelete(array &$aResponse) : void
+    {
+        if (empty($aResponse['Result'])) {
+            return;
+        }
+        $oActions = \RainLoop\Api::Actions();
+        $oMain = $oActions->getMainAccountFromToken(false);
+        if (!$oMain) {
+            return;
+        }
+        $email = \strtolower(\SnappyMail\IDN::emailToAscii(\trim((string) $oActions->GetActionParam('emailToDelete', ''))));
+        if ($email && $this->isSupportedEmail($email)) {
+            $oActions->StorageProvider()->Clear($oMain, StorageType::CONFIG, $this->tokenStorageKey($email));
         }
     }
 
@@ -326,4 +444,252 @@ class LoginO365Plugin extends \RainLoop\Plugins\AbstractPlugin
         $data = \json_decode($json, true);
         return \is_array($data) ? $data : null;
     }
+
+    /**
+     * JSON action called by JS to obtain an MS authorize URL with signed state.
+     * This avoids exposing any signing secret to JS and keeps redirect_uri consistent with server logic.
+     */
+    public function DoLoginO365AuthUrl() : array
+    {
+        $oActions = \RainLoop\Api::Actions();
+
+        $op = (string) $this->jsonParam('op', 'login');
+        if (!\in_array($op, ['login', 'add'], true)) {
+            return $this->jsonResponse(__FUNCTION__, false);
+        }
+
+        $email = \strtolower(\trim((string) $this->jsonParam('email', '')));
+        $name = \trim((string) $this->jsonParam('name', ''));
+        $returnHash = (string) $this->jsonParam('return', '');
+
+        if ($returnHash && !\str_starts_with($returnHash, '#')) {
+            $returnHash = '';
+        }
+
+        // For add-account flow, require a logged-in main account (we must write to its additionalaccounts storage).
+        $oMainAccount = null;
+        if ('add' === $op) {
+            $oMainAccount = $oActions->getMainAccountFromToken(false);
+            if (!$oMainAccount) {
+                return $this->jsonResponse(__FUNCTION__, false);
+            }
+        }
+
+        // Optional server-side guard: only permit supported consumer domains unless configured otherwise.
+        if ($email && !$this->isSupportedEmail($email)) {
+            return $this->jsonResponse(__FUNCTION__, false);
+        }
+
+        $oConfig = $this->Config();
+        $client_id = \trim($oConfig->Get('plugin', 'client_id', ''));
+        if (!$client_id) {
+            return $this->jsonResponse(__FUNCTION__, false);
+        }
+
+        $nonce = $this->b64url(\random_bytes(16));
+        // Store nonce server-side to prevent replay; consumed on callback.
+        $oActions->StorageProvider()->Put(
+            null,
+            StorageType::NOBODY,
+            $this->stateNonceKey($nonce),
+            (string) \time()
+        );
+
+        $payload = [
+            'v' => 1,
+            'op' => $op,
+            'csrf' => \RainLoop\Utils::GetCsrfToken(),
+            'nonce' => $nonce,
+            'ts' => \time()
+        ];
+        if ('add' === $op && $oMainAccount) {
+            $payload['main'] = $oMainAccount->Email();
+            if ($name) {
+                $payload['name'] = \substr($name, 0, 100);
+            }
+            if ($returnHash) {
+                $payload['return'] = \substr($returnHash, 0, 200);
+            }
+        }
+
+        $state = $this->signState($payload);
+        $tenant = $oConfig->Get('plugin', 'tenant', 'common');
+        $redirectUri = $this->redirectUri();
+
+        $params = [
+                'response_type' => 'code',
+                'client_id' => $client_id,
+                'redirect_uri' => $redirectUri,
+                'scope' => \implode(' ', [
+                    'openid',
+                    'offline_access',
+                    'email',
+                    'profile',
+                    'https://outlook.office.com/IMAP.AccessAsUser.All',
+                    'https://outlook.office.com/SMTP.Send',
+                ]),
+                'state' => $state,
+                // Helps MS UI prefill, but does not change server-side validation.
+        ];
+        if ($email) {
+            $params['login_hint'] = $email;
+        }
+        $authUrl = \str_replace('{{tenant}}', $tenant, static::AUTH_URI)
+            . '?'
+            . \http_build_query($params, '', '&', PHP_QUERY_RFC3986);
+
+        return $this->jsonResponse(__FUNCTION__, [
+            'authUrl' => $authUrl
+        ]);
+    }
+
+    private function isSupportedEmail(string $email) : bool
+    {
+        if ((bool)$this->Config()->Get('plugin', 'allow_any_domain', false)) {
+            return \str_contains($email, '@');
+        }
+        return \str_ends_with($email, '@hotmail.com')
+            || \str_ends_with($email, '@outlook.com')
+            || \str_ends_with($email, '@live.com');
+    }
+
+    /**
+     * Build absolute base URL (works behind nginx reverse proxy).
+     */
+    private function baseUrl() : string
+    {
+        $scheme = (!empty($_SERVER['HTTP_X_FORWARDED_PROTO']))
+            ? $_SERVER['HTTP_X_FORWARDED_PROTO']
+            : ((!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off') ? 'https' : 'http');
+
+        $host = $_SERVER['HTTP_HOST'] ?? $_SERVER['SERVER_NAME'] ?? '';
+        if (!$host) {
+            throw new \RuntimeException('Cannot determine HTTP_HOST');
+        }
+        return $scheme . '://' . $host;
+    }
+
+    /**
+     * Redirect URI used for the Azure app registration.
+     * When plugin.personal=true -> "/?LoginO365"
+     * When plugin.personal=false -> "/LoginO365"
+     */
+    private function redirectUri() : string
+    {
+        $base = \rtrim($this->baseUrl(), '/');
+        $useQuery = (bool)$this->Config()->Get('plugin', 'personal', false);
+        return $useQuery ? ($base . '/?LoginO365') : ($base . '/LoginO365');
+    }
+
+    private function tokenStorageKey(string $emailLower) : string
+    {
+        // Stored under MAIN account StorageType::CONFIG (encrypted with main CryptKey).
+        // Email is hashed to avoid path/encoding issues across storage backends.
+        return 'login-o365.tokens.' . \sha1($emailLower);
+    }
+
+    private function storeAccountTokens(MainAccount $oMainAccount, string $email, array $tokenBundle) : void
+    {
+        $emailLower = \strtolower(\SnappyMail\IDN::emailToAscii($email));
+        \RainLoop\Api::Actions()->StorageProvider()->Put(
+            $oMainAccount,
+            StorageType::CONFIG,
+            $this->tokenStorageKey($emailLower),
+            \SnappyMail\Crypt::EncryptToJSON($tokenBundle, $oMainAccount->CryptKey())
+        );
+    }
+
+    private function stateNonceKey(string $nonce) : string
+    {
+        return 'login-o365.state.' . $nonce;
+    }
+
+    private function b64url(string $bin) : string
+    {
+        return \rtrim(\strtr(\base64_encode($bin), '+/', '-_'), '=');
+    }
+
+    private function b64urlDecode(string $b64url) /*: string|false*/
+    {
+        $pad = (4 - (\strlen($b64url) % 4)) % 4;
+        return \base64_decode(\strtr($b64url . \str_repeat('=', $pad), '-_', '+/'), true);
+    }
+
+    private function stateHmacKey() : string
+    {
+        // Uses the plugin client_secret (server-side only) as HMAC key.
+        // This prevents any user-controlled tampering of the state payload.
+        $key = \trim($this->Config()->getDecrypted('plugin', 'client_secret', ''));
+        if (!$key) {
+            // Fallback for misconfiguration; keeps behavior deterministic.
+            $key = 'login-o365';
+        }
+        return $key;
+    }
+
+    private function signState(array $payload) : string
+    {
+        $json = \json_encode($payload);
+        if (!$json) {
+            $json = '{}';
+        }
+        $payloadB64 = $this->b64url($json);
+        $sig = \hash_hmac('sha256', $payloadB64, $this->stateHmacKey(), true);
+        return $payloadB64 . '.' . $this->b64url($sig);
+    }
+
+    /**
+     * Verify signature + CSRF + nonce, then consumes nonce to prevent replay.
+     * Returns decoded payload on success, null on failure.
+     */
+    private function verifyAndConsumeState(string $state) : ?array
+    {
+        $parts = \explode('.', $state, 2);
+        if (2 !== \count($parts)) {
+            return null;
+        }
+        [$payloadB64, $sigB64] = $parts;
+        $sig = $this->b64urlDecode($sigB64);
+        if ($sig === false) {
+            return null;
+        }
+
+        $expected = \hash_hmac('sha256', $payloadB64, $this->stateHmacKey(), true);
+        if (!\hash_equals($expected, $sig)) {
+            return null;
+        }
+
+        $payloadJson = $this->b64urlDecode($payloadB64);
+        if ($payloadJson === false) {
+            return null;
+        }
+        $payload = \json_decode($payloadJson, true);
+        if (!\is_array($payload) || empty($payload['csrf']) || empty($payload['nonce']) || empty($payload['op'])) {
+            return null;
+        }
+
+        // Must match the current browser session.
+        if ($payload['csrf'] !== \RainLoop\Utils::GetCsrfToken()) {
+            return null;
+        }
+
+        // Replay protection: nonce must exist server-side and is consumed once.
+        $oActions = \RainLoop\Api::Actions();
+        $key = $this->stateNonceKey((string) $payload['nonce']);
+        $seen = $oActions->StorageProvider()->Get(null, StorageType::NOBODY, $key);
+        if (!$seen) {
+            return null;
+        }
+
+        $ts = (int) ($payload['ts'] ?? 0);
+        if ($ts && \abs(\time() - $ts) > 900) { // 15 minutes
+            // Expired: clear nonce to avoid accumulating stale entries.
+            $oActions->StorageProvider()->Clear(null, StorageType::NOBODY, $key);
+            return null;
+        }
+
+        $oActions->StorageProvider()->Clear(null, StorageType::NOBODY, $key);
+
+        return $payload;
+    }
 }