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Single sign-on with MSAL.js

  • Članak

Single sign-on (SSO) provides a more seamless experience by reducing the number of times a user is asked for credentials. Users enter their credentials once, and the established session can be reused by other applications on the same device without further prompting.

Microsoft Entra ID enables SSO by setting a session cookie when a user authenticates for the first time. MSAL.js also caches the ID tokens and access tokens of the user in the browser storage per application domain. The two mechanisms, Microsoft Entra session cookie and Microsoft Authentication Library (MSAL) cache, are independent of each other but work together to provide SSO behavior.

SSO between browser tabs for the same app

When a user has an application open in several tabs and signs in on one of them, they can be signed into the same app open on other tabs without being prompted. To do so, you need to set the cacheLocation in MSAL.js configuration object to localStorage as shown in the following example:

const config = {
  auth: {
    clientId: "1111-2222-3333-4444-55555555",
  },
  cache: {
    cacheLocation: "localStorage",
  },
};

const msalInstance = new msal.PublicClientApplication(config);

In this case, application instances in different browser tabs make use of the same MSAL cache, thus sharing the authentication state between them. You can also use MSAL events for updating application instances when a user logs in from another browser tab or window. For more information, see: Syncing logged in state across tabs and windows

SSO between different apps

When a user authenticates, a session cookie is set on the Microsoft Entra domain in the browser. MSAL.js relies on this session cookie to provide SSO for the user between different applications. In particular, MSAL.js offers the ssoSilent method to sign-in the user and obtain tokens without an interaction. However, if the user has multiple user accounts in a session with Microsoft Entra ID, they're then prompted to pick an account to sign in with. As such, there are two ways to achieve SSO using ssoSilent method.

With user hint

To improve performance and ensure that the authorization server will look for the correct account session, you can pass one of the following options in the request object of the ssoSilent method to obtain the token silently.

  • login_hint, which can be retrieved from the account object username property or the upn claim in the ID token. If your app is authenticating users with B2C, see: Configure B2C user-flows to emit username in ID tokens
  • Session ID, sid, which can be retrieved from idTokenClaims of an account object.
  • account, which can be retrieved from using one the account methods

We recommended to using the login_hint optional ID token claim provided to ssoSilent as loginHint as it is the most reliable account hint of silent and interactive requests.

Using a login hint

The login_hint optional claim provides a hint to Microsoft Entra ID about the user account attempting to sign in. To bypass the account selection prompt typically shown during interactive authentication requests, provide the loginHint as shown:

const silentRequest = {
    scopes: ["User.Read", "Mail.Read"],
    loginHint: "user@contoso.com"
};

try {
    const loginResponse = await msalInstance.ssoSilent(silentRequest);
} catch (err) {
    if (err instanceof InteractionRequiredAuthError) {
        const loginResponse = await msalInstance.loginPopup(silentRequest).catch(error => {
            // handle error
        });
    } else {
        // handle error
    }
}

In this example, loginHint contains the user's email or UPN, which is used as a hint during interactive token requests. The hint can be passed between applications to facilitate silent SSO, where application A can sign in a user, read the loginHint, and then send the claim and the current tenant context to application B. Microsoft Entra ID will attempt to pre-fill the sign-in form or bypass the account selection prompt and directly proceed with the authentication process for the specified user.

If the information in the login_hint claim doesn't match any existing user, they're redirected to go through the standard sign-in experience, including account selection.

Using a session ID

To use a session ID, add sid as an optional claim to your app's ID tokens. The sid claim allows an application to identify a user's Microsoft Entra session independent of their account name or username. To learn how to add optional claims like sid, see Provide optional claims to your app. Use the session ID (SID) in silent authentication requests you make with ssoSilent in MSAL.js.

const request = {
  scopes: ["user.read"],
  sid: sid,
};

 try {
    const loginResponse = await msalInstance.ssoSilent(request);
} catch (err) {
    if (err instanceof InteractionRequiredAuthError) {
        const loginResponse = await msalInstance.loginPopup(request).catch(error => {
            // handle error
        });
    } else {
        // handle error
    }
}

Using an account object

If you know the user account information, you can also retrieve the user account by using the getAccountByUsername() or getAccountByHomeId() methods:

const username = "test@contoso.com";
const myAccount  = msalInstance.getAccountByUsername(username);

const request = {
    scopes: ["User.Read"],
    account: myAccount
};

try {
    const loginResponse = await msalInstance.ssoSilent(request);
} catch (err) {
    if (err instanceof InteractionRequiredAuthError) {
        const loginResponse = await msalInstance.loginPopup(request).catch(error => {
            // handle error
        });
    } else {
        // handle error
    }
}

Without user hint

You can attempt to use the ssoSilent method without passing any account, sid or login_hint as shown in the following code:

const request = {
    scopes: ["User.Read"]
};

try {
    const loginResponse = await msalInstance.ssoSilent(request);
} catch (err) {
    if (err instanceof InteractionRequiredAuthError) {
        const loginResponse = await msalInstance.loginPopup(request).catch(error => {
            // handle error
        });
    } else {
        // handle error
    }
}

However, there's a likelihood of silent sign-in errors if the application has multiple users in a single browser session or if the user has multiple accounts for that single browser session. The following error may be displayed if multiple accounts are available:

InteractionRequiredAuthError: interaction_required: AADSTS16000: Either multiple user identities are available for the current request or selected account is not supported for the scenario.

The error indicates that the server couldn't determine which account to sign into, and will require either one of the parameters in the previous example (account, login_hint, sid) or an interactive sign-in to choose the account.

Considerations when using ssoSilent

Redirect URI (reply URL)

For better performance and to help avoid issues, set the redirectUri to a blank page or other page that doesn't use MSAL.

  • If the application users only popup and silent methods, set the redirectUri on the PublicClientApplication configuration object.
  • If the application also uses redirect methods, set the redirectUri on a per-request basis.

Third-party cookies

ssoSilent attempts to open a hidden iframe and reuse an existing session with Microsoft Entra ID. This won't work in browsers that block third-party cookies such as Safari, and will lead to an interaction error:

InteractionRequiredAuthError: login_required: AADSTS50058: A silent sign-in request was sent but no user is signed in. The cookies used to represent the user's session were not sent in the request to Azure AD

To resolve the error, the user must create an interactive authentication request using the loginPopup() or loginRedirect(). In some cases, the prompt value none can be used together with an interactive MSAL.js method to achieve SSO. See Interactive requests with prompt=none for more. If you already have the user's sign-in information, you can pass either the loginHint or sid optional parameters to sign-in a specific account.

Negating SSO with prompt=login

If you prefer Microsoft Entra ID to prompt the user for entering their credentials despite an active session with the authorization server, you can use the login prompt parameter in requests with MSAL.js. See MSAL.js prompt behavior for more.

Sharing authentication state between ADAL.js and MSAL.js

MSAL.js brings feature parity with ADAL.js for Microsoft Entra authentication scenarios. To make the migration from ADAL.js to MSAL.js easy and share authentication state between apps, the library reads the ID token representing user’s session in ADAL.js cache. To take advantage of this when migrating from ADAL.js, you'll need to ensure that the libraries are using localStorage for caching tokens. Set the cacheLocation to localStorage in both the MSAL.js and ADAL.js configuration at initialization as follows:


// In ADAL.js
window.config = {
  clientId: "1111-2222-3333-4444-55555555",
  cacheLocation: "localStorage",
};

var authContext = new AuthenticationContext(config);

// In latest MSAL.js version
const config = {
  auth: {
    clientId: "1111-2222-3333-4444-55555555",
  },
  cache: {
    cacheLocation: "localStorage",
  },
};

const msalInstance = new msal.PublicClientApplication(config);

Next steps

For more information about SSO, see: