diff --git a/src/auth/auth.ts b/src/auth/auth.ts
index 032f955fdd..77d8290e03 100755
--- a/src/auth/auth.ts
+++ b/src/auth/auth.ts
@@ -70,6 +70,8 @@ export interface DecodedIdToken {
       [key: string]: any;
     };
     sign_in_provider: string;
+    sign_in_second_factor?: string;
+    second_factor_identifier?: string;
     [key: string]: any;
   };
   iat: number;
diff --git a/src/index.d.ts b/src/index.d.ts
index 151f787466..17aa17db0a 100755
--- a/src/index.d.ts
+++ b/src/index.d.ts
@@ -544,6 +544,48 @@ declare namespace admin.auth {
     toJSON(): Object;
   }
 
+  /**
+   * Interface representing the common properties of a user enrolled second factor.
+   */
+  interface MultiFactorInfo {
+  
+    /**
+     * The ID of the enrolled second factor. This ID is unique to the user.
+     */
+    uid: string;
+
+    /**
+     * The optional display name of the enrolled second factor.
+     */
+    displayName?: string;
+
+    /**
+     * The optional date the second factor was enrolled, formatted as a UTC string.
+     */
+    enrollmentTime?: string;
+
+    /**
+     * The type identifier of the second factor. For SMS second factors, this is `phone`.
+     */
+    factorId: string;
+
+    /**
+     * @return A JSON-serializable representation of this object.
+     */
+    toJSON(): Object;
+  }
+
+  /**
+   * Interface representing a phone specific user enrolled second factor.
+   */
+  interface PhoneMultiFactorInfo extends MultiFactorInfo {
+
+    /**
+     * The phone number associated with a phone second factor.
+     */
+    phoneNumber: string;
+  }
+
   /**
    * Interface representing a user.
    */
@@ -639,14 +681,21 @@ declare namespace admin.auth {
      */
     tenantId?: string | null;
 
+    /**
+     * The multi-factor related properties for the current user, if available.
+     */
     multiFactor?: {
-      enrolledFactors: Array<{
-        uid: string;
-        phoneNumber: string;
-        displayName?: string;
-        enrollmentTime?: string;
-        factorId: string;
-      }>;
+
+      /**
+       * List of second factors enrolled with the current user.
+       * Currently only phone second factors are supported.
+       */
+      enrolledFactors: PhoneMultiFactorInfo[];
+
+      /**
+       * @return A JSON-serializable representation of this multi-factor object.
+       */
+      toJSON(): Object;
     };
 
     /**
@@ -655,6 +704,46 @@ declare namespace admin.auth {
     toJSON(): Object;
   }
 
+  /**
+   * Interface representing common properties of a user enrolled second factor
+   * for an `UpdateRequest`.
+   */
+  interface UpdateMultiFactorInfoRequest {
+  
+    /**
+     * The ID of the enrolled second factor. This ID is unique to the user. When not provided,
+     * a new one is provisioned by the Auth server.
+     */
+    uid?: string;
+
+    /**
+     * The optional display name for an enrolled second factor.
+     */
+    displayName?: string;
+
+    /**
+     * The optional date the second factor was enrolled, formatted as a UTC string.
+     */
+    enrollmentTime?: string;
+
+    /**
+     * The type identifier of the second factor. For SMS second factors, this is `phone`.
+     */
+    factorId: string;
+  }
+
+  /**
+   * Interface representing a phone specific user enrolled second factor
+   * for an `UpdateRequest`.
+   */
+  interface UpdatePhoneMultiFactorInfoRequest extends UpdateMultiFactorInfoRequest {
+
+    /**
+     * The phone number associated with a phone second factor.
+     */
+    phoneNumber: string;
+  }
+
   /**
    * Interface representing the properties to update on the provided user.
    */
@@ -696,17 +785,49 @@ declare namespace admin.auth {
      */
     photoURL?: string | null;
 
+    /**
+     * The user's updated multi-factor related properties.
+     */
     multiFactor?: {
-      enrolledFactors: Array<{
-        uid?: string;
-        phoneNumber: string;
-        displayName?: string;
-        enrollmentTime?: string;
-        factorId: string;
-      }> | null;
+
+      /**
+       * The updated list of enrolled second factors. The provided list overwrites the user's
+       * existing list of second factors.
+       * When null is passed, all of the user's existing second factors are removed.
+       */
+      enrolledFactors: UpdatePhoneMultiFactorInfoRequest[] | null;
     };
   }
 
+  /**
+   * Interface representing base properties of a user enrolled second factor for a
+   * `CreateRequest`.
+   */
+  interface CreateMultiFactorInfoRequest {
+
+    /**
+     * The optional display name for an enrolled second factor.
+     */
+    displayName?: string;
+
+    /**
+     * The type identifier of the second factor. For SMS second factors, this is `phone`.
+     */
+    factorId: string;
+  }
+
+  /**
+   * Interface representing a phone specific user enrolled second factor for a
+   * `CreateRequest`.
+   */
+  interface CreatePhoneMultiFactorInfoRequest extends CreateMultiFactorInfoRequest {
+
+    /**
+     * The phone number associated with a phone second factor.
+     */
+    phoneNumber: string;
+  }
+
   /**
    * Interface representing the properties to set on a new user record to be
    * created.
@@ -718,12 +839,15 @@ declare namespace admin.auth {
      */
     uid?: string;
 
+    /**
+     * The user's multi-factor related properties.
+     */
     multiFactor?: {
-      enrolledFactors: Array<{
-        phoneNumber: string;
-        displayName?: string;
-        factorId: string;
-      }>;
+
+      /**
+       * The user's list of enrolled second factors.
+       */
+      enrolledFactors: CreatePhoneMultiFactorInfoRequest[];
     };
   }
 
@@ -791,6 +915,19 @@ declare namespace admin.auth {
        */
       sign_in_provider: string;
 
+      /**
+       * The type identifier or `factorId` of the second factor, provided the
+       * ID token was obtained from a multi-factor authenticated user.
+       * For phone, this is `“phone”`.
+       */
+      sign_in_second_factor?: string;
+
+      /**
+       * The `uid` of the second factor used to sign in, provided the
+       * ID token was obtained from a multi-factor authenticated user.
+       */
+      second_factor_identifier?: string;
+  
       /**
        * The ID of the tenant the user belongs to, if available.
        */
@@ -1029,14 +1166,15 @@ declare namespace admin.auth {
      */
     tenantId?: string | null;
 
+    /**
+     * The multi-factor related properties for the imported user if available.
+     */
     multiFactor?: {
-      enrolledFactors: Array<{
-        uid: string;
-        phoneNumber: string;
-        displayName?: string;
-        enrollmentTime?: string;
-        factorId: string;
-      }>;
+    
+      /**
+       * List of enrolled second factors on the user to import.
+       */
+      enrolledFactors: PhoneMultiFactorInfo[];
     };
   }