[Home](./index.md) > [@firebase/auth](./auth.md) > [User](./auth.user.md) > [tenantId](./auth.user.tenantid.md) ## User.tenantId property The user's tenant ID. Signature: ```typescript readonly tenantId: string | null; ``` ## Remarks This is a read-only property, which indicates the tenant ID used to sign in the user. This is null if the user is signed in from the parent project. ## Example ```javascript // Set the tenant ID on Auth instance. auth.tenantId = 'TENANT_PROJECT_ID'; // All future sign-in request now include tenant ID. const result = await signInWithEmailAndPassword(auth, email, password); // result.user.tenantId should be 'TENANT_PROJECT_ID'. ```