Custom flows

A custom flow refers to a user flow created entirely from scratch using the Clerk API. If Clerk's prebuilt components don't meet your specific needs or if you require more control over the logic, you can rebuild the existing Clerk flows using the Clerk API.

How authentication flows work in Clerk

Before building custom authentication flows, read the following sections to get a general understanding of how authentication flows work in Clerk.

Sign-up flow

The SignUp object is the pivotal concept in the sign-up process. It is used to gather the user's information, verify their email address or phone number, add OAuth accounts, and finally, convert them into a User.

Every SignUp has a set of requirements it must meet before it is turned into a User. These requirements are defined by the instance settings you selected in the Clerk Dashboard. For example, on the Email, Phone, Username page, configuring passwords or email links or even both as the authentication strategies.

Once all requirements are met, the SignUp will turn into a new User, and an active session for that User will be created on the current Client.

Don't worry about collecting all the required fields at once and passing them to a single request. The API is designed to accommodate progressive multi-step sign-up forms.

The following steps outline the sign-up process:

1. Initiate the sign-up process by collecting the user's authentication information and passing the appropriate parameters to the create() method.
2. Prepare the verification.
3. Attempt to complete the verification.
4. If the verification is successful, set the newly created session as the active session by passing the SignIn.createdSessionId to the setActive() method on the Clerk object.

The state of a SignUp

The SignUp object will show the state of the current sign-up in the status property.

If you need further help on where things are and what you need to do next, you can also consult the required_fields, optional_fields, and missingFields properties.

Name	Description
requiredFields	All fields that must be collected before the SignUp converts into a User.
optionalFields	All fields that can be collected, but are not necessary to convert the SignUp into a User.
missingFields	A subset of requiredFields. It contains all fields that still need to be collected before a SignUp can be converted into a User. Note that this property will be updated dynamically. As you add more fields to the SignUp, they will be removed. Once this property is empty, your SignUp will automatically convert into a User.

Verified fields

Some properties of the SignUp, such as emailAddress and phoneNumber, must be verified before they are fully added to the SignUp object.

The SignUp object will show the state of verification in the following properties:

Name	Description
unverifiedFields	A list of all User attributes that need to be verified and are pending verification. This is a list that gets updated dynamically. When verification for all required fields has been successfully completed, this value will become an empty array.
verifications	An object that describes the current state of verification for the SignUp. There are currently three different keys: email_address, phone_number, and external_account.

Sign-in flow

The SignIn object is the pivotal concept in the sign-in process.

Sign-ins are initiated by creating a SignIn object on the current Client. If the sign-in is successfully authenticated, it will transform into an active session for that User on the current Client.

The following steps outline the sign-in process:

1. Initiate the sign-in process by collecting the user's authentication information and passing the appropriate parameters to the create() method.
2. Prepare the first factor verification. Users must complete a first factor verification to prove their identity. This can be something like providing a password, an email link, a one-time code (OTP), a web3 wallet public address, or providing proof of their identity through an external social account (SSO/OAuth).
3. Attempt to complete the first factor verification.
4. Optionally, if you have enabled multi-factor for your application, you will need to prepare the second factor verification for users who have set up 2FA for their account.
5. Attempt to complete the second factor verification.
6. If verification is successful, set the newly created session as the active session by passing the SignIn.createdSessionId to the setActive() method on the Clerk object.

Next steps

Now that you have a general understanding of how authentication flows work in Clerk, you can start building your custom flows. To get started, choose the guide that best fits your needs from the navigation on the left.