[Home](./index.md) > [@firebase/auth](./auth.md) > [MultiFactorAssertion](./auth.multifactorassertion.md) ## MultiFactorAssertion interface The base class for asserting ownership of a second factor. Signature: ```typescript export interface MultiFactorAssertion ``` ## Remarks This is used to facilitate enrollment of a second factor on an existing user or sign-in of a user who already verified the first factor. ## Properties | Property | Type | Description | | --- | --- | --- | | [factorId](./auth.multifactorassertion.factorid.md) | [FactorId](./auth.factorid.md) | The identifier of the second factor. |