feat(auth): Add ability to link a federated ID with the updateUser() method.

etc/firebase-admin.api.md

@@ -300,6 +300,8 @@ export namespace auth {
         password?: string;
         phoneNumber?: string | null;
         photoURL?: string | null;
+        providersToUnlink?: string[];
+        providerToLink?: UserProvider;
     }
     export interface UpdateTenantRequest {
         anonymousSignInEnabled?: boolean;
@@ -365,6 +367,14 @@ export namespace auth {
         creationTime?: string;
         lastSignInTime?: string;
     }
+    export interface UserProvider {
+        displayName?: string;
+        email?: string;
+        phoneNumber?: string;
+        photoURL?: string;
+        providerId?: string;
+        uid?: string;
+    }
     export interface UserProviderRequest {
         displayName?: string;
         email?: string;
@@ -393,6 +403,7 @@ export namespace auth {
         tokensValidAfterTime?: string;
         uid: string;
     }
+    {};
 }
 
 // @public (undocumented)

src/auth/auth-api-request.ts

@@ -403,6 +403,8 @@ function validateCreateEditRequest(request: any, writeOperationType: WriteOperat
     phoneNumber: true,
     customAttributes: true,
     validSince: true,
+    // Pass linkProviderUserInfo only for updates (i.e. not for uploads.)
+    linkProviderUserInfo: !uploadAccountRequest,
     // Pass tenantId only for uploadAccount requests.
     tenantId: uploadAccountRequest,
     passwordHash: uploadAccountRequest,
@@ -551,6 +553,12 @@ function validateCreateEditRequest(request: any, writeOperationType: WriteOperat
       validateProviderUserInfo(providerUserInfoEntry);
     });
   }
+
+  // linkProviderUserInfo must be a (single) UserProvider value.
+  if (typeof request.linkProviderUserInfo !== 'undefined') {
+    validateProviderUserInfo(request.linkProviderUserInfo);
+  }
+
   // mfaInfo is used for importUsers.
   // mfa.enrollments is used for setAccountInfo.
   // enrollments has to be an array of valid AuthFactorInfo requests.
@@ -1306,6 +1314,33 @@ export abstract class AbstractAuthRequestHandler {
           'Properties argument must be a non-null object.',
         ),
       );
+    } else if (validator.isNonNullObject(properties.providerToLink)) {
+      // TODO(rsgowman): These checks overlap somewhat with
+      // validateProviderUserInfo. It may be possible to refactor a bit.
+      if (!validator.isNonEmptyString(properties.providerToLink.providerId)) {
+        throw new FirebaseAuthError(
+          AuthClientErrorCode.INVALID_ARGUMENT,
+          'providerToLink.providerId of properties argument must be a non-empty string.');
+      }
+      if (!validator.isNonEmptyString(properties.providerToLink.uid)) {
+        throw new FirebaseAuthError(
+          AuthClientErrorCode.INVALID_ARGUMENT,
+          'providerToLink.uid of properties argument must be a non-empty string.');
+      }
+    } else if (typeof properties.providersToUnlink !== 'undefined') {
+      if (!validator.isArray(properties.providersToUnlink)) {
+        throw new FirebaseAuthError(
+          AuthClientErrorCode.INVALID_ARGUMENT,
+          'providersToUnlink of properties argument must be an array of strings.');
+      }
+
+      properties.providersToUnlink.forEach((providerId) => {
+        if (!validator.isNonEmptyString(providerId)) {
+          throw new FirebaseAuthError(
+            AuthClientErrorCode.INVALID_ARGUMENT,
+            'providersToUnlink of properties argument must be an array of strings.');
+        }
+      });
     }
 
     // Build the setAccountInfo request.
@@ -1340,13 +1375,25 @@ export abstract class AbstractAuthRequestHandler {
     // It will be removed from the backend request and an additional parameter
     // deleteProvider: ['phone'] with an array of providerIds (phone in this case),
     // will be passed.
-    // Currently this applies to phone provider only.
     if (request.phoneNumber === null) {
-      request.deleteProvider = ['phone'];
+      request.deleteProvider ? request.deleteProvider.push('phone') : request.deleteProvider = ['phone'];
       delete request.phoneNumber;
-    } else {
-      // Doesn't apply to other providers in admin SDK.
-      delete request.deleteProvider;
+    }
+
+    if (typeof(request.providerToLink) !== 'undefined') {
+      request.linkProviderUserInfo = deepCopy(request.providerToLink);
+      delete request.providerToLink;
+
+      request.linkProviderUserInfo.rawId = request.linkProviderUserInfo.uid;
+      delete request.linkProviderUserInfo.uid;
+    }
+
+    if (typeof(request.providersToUnlink) !== 'undefined') {
+      if (!validator.isArray(request.deleteProvider)) {
+        request.deleteProvider = [];
+      }
+      request.deleteProvider = request.deleteProvider.concat(request.providersToUnlink);
+      delete request.providersToUnlink;
     }
 
     // Rewrite photoURL to photoUrl.

src/auth/auth.ts

@@ -15,6 +15,7 @@
  * limitations under the License.
  */
 
+import { deepCopy } from '../utils/deep-copy';
 import { UserRecord } from './user-record';
 import {
   isUidIdentifier, isEmailIdentifier, isPhoneIdentifier, isProviderIdentifier,
@@ -381,6 +382,50 @@ export class BaseAuth<T extends AbstractAuthRequestHandler> implements BaseAuthI
    * @return {Promise<UserRecord>} A promise that resolves with the modified user record.
    */
   public updateUser(uid: string, properties: UpdateRequest): Promise<UserRecord> {
+    // Although we don't really advertise it, we want to also handle linking of
+    // non-federated idps with this call. So if we detect one of them, we'll
+    // adjust the properties parameter appropriately. This *does* imply that a
+    // conflict could arise, e.g. if the user provides a phoneNumber property,
+    // but also provides a providerToLink with a 'phone' provider id. In that
+    // case, we'll throw an error.
+    properties = deepCopy(properties);
+
+    if (properties?.providerToLink) {
+      if (properties.providerToLink.providerId === 'email') {
+        if (typeof properties.email !== 'undefined') {
+          throw new FirebaseAuthError(
+            AuthClientErrorCode.INVALID_ARGUMENT,
+            "Both UpdateRequest.email and UpdateRequest.providerToLink.providerId='email' were set. To "
+            + 'link to the email/password provider, only specify the UpdateRequest.email field.');
+        }
+        properties.email = properties.providerToLink.uid;
+        delete properties.providerToLink;
+      } else if (properties.providerToLink.providerId === 'phone') {
+        if (typeof properties.phoneNumber !== 'undefined') {
+          throw new FirebaseAuthError(
+            AuthClientErrorCode.INVALID_ARGUMENT,
+            "Both UpdateRequest.phoneNumber and UpdateRequest.providerToLink.providerId='phone' were set. To "
+            + 'link to a phone provider, only specify the UpdateRequest.phoneNumber field.');
+        }
+        properties.phoneNumber = properties.providerToLink.uid;
+        delete properties.providerToLink;
+      }
+    }
+    if (properties?.providersToUnlink) {
+      if (properties.providersToUnlink.indexOf('phone') !== -1) {
+        // If we've been told to unlink the phone provider both via setting
+        // phoneNumber to null *and* by setting providersToUnlink to include
+        // 'phone', then we'll reject that. Though it might also be reasonable
+        // to relax this restriction and just unlink it.
+        if (properties.phoneNumber === null) {
+          throw new FirebaseAuthError(
+            AuthClientErrorCode.INVALID_ARGUMENT,
+            "Both UpdateRequest.phoneNumber=null and UpdateRequest.providersToUnlink=['phone'] were set. To "
+            + 'unlink from a phone provider, only specify the UpdateRequest.phoneNumber=null field.');
+        }
+      }
+    }
+
     return this.authRequestHandler.updateExistingAccount(uid, properties)
       .then((existingUid) => {
         // Return the corresponding user record.

src/auth/index.ts

@@ -153,6 +153,42 @@ export namespace auth {
     phoneNumber: string;
   }
 
+  /**
+   * Represents a user identity provider that can be associated with a Firebase user.
+   */
+  interface UserProvider {
+
+    /**
+     * The user identifier for the linked provider.
+     */
+    uid?: string;
+
+    /**
+     * The display name for the linked provider.
+     */
+    displayName?: string;
+
+    /**
+     * The email for the linked provider.
+     */
+    email?: string;
+
+    /**
+     * The phone number for the linked provider.
+     */
+    phoneNumber?: string;
+
+    /**
+     * The photo URL for the linked provider.
+     */
+    photoURL?: string;
+
+    /**
+     * The linked provider ID (for example, "google.com" for the Google provider).
+     */
+    providerId?: string;
+  }
+
   /**
    * Interface representing a user.
    */
@@ -384,6 +420,26 @@ export namespace auth {
      * The user's updated multi-factor related properties.
      */
     multiFactor?: MultiFactorUpdateSettings;
+
+    /**
+     * Links this user to the specified provider.
+     *
+     * Linking a provider to an existing user account does not invalidate the
+     * refresh token of that account. In other words, the existing account
+     * would continue to be able to access resources, despite not having used
+     * the newly linked provider to log in. If you wish to force the user to
+     * authenticate with this new provider, you need to (a) revoke their
+     * refresh token (see
+     * https://firebase.google.com/docs/auth/admin/manage-sessions#revoke_refresh_tokens),
+     * and (b) ensure no other authentication methods are present on this
+     * account.
+     */
+    providerToLink?: UserProvider;
+
+    /**
+     * Unlinks this user from the specified providers.
+     */
+    providersToUnlink?: string[];
   }
 
   /**