This document guides you through the implementation flow and checklist items required when integrating Kakao Sync into your service.

Kakao Sync works based on Kakao Login. When you adopt the Simple Signup feature of Kakao Sync, users can also consent to your service terms on the Consent screen, so they can sign up for your service with a single click.

Even if a user successfully completes Kakao Login, service signup is not completed unless your service creates a member in the service database or links the user with an existing member. After retrieving user information and checking service terms consent details, you must implement signup or login processing according to your service policy.

If development is difficult, you can also use a shopping mall hosting service. See Guide for e-commerce platforms.

The following is the basic flow of Kakao Sync Simple Signup using the REST API method. Refer to the step-by-step explanation together with the diagram below.

Kakao Sync Simple Signup process

When a user selects the [Start with Kakao] button, your service calls the Get authorization code API for Kakao Login.

The Kakao authentication server provides Kakao Account authentication and the Consent screen to the user. Depending on your app settings, the Kakao Sync Consent screen may also display the following items.

• Consent to providing user information required for service signup
• Consent to service terms
• Consent to adding a Kakao Talk Channel

When the user consents to the consent items and service terms, the Kakao authentication server returns an authorization code to the configured Redirect URI.

Your service server calls the Get token API with the received authorization code to issue an access token.

An authorization code can be used only once. If the token request fails, do not retry with the same authorization code. Instead, have the user log in again.

Your service server calls the Retrieve user information API with the access token. The service user ID (id) in the response is an identifier to identify Kakao Sync users.

From the Retrieve user information response, your service can check the following.

• Service user ID (id)
• User information that the user consented to provide
• Consent details that the user consented to
• Time of the user signing up through Kakao Sync Simple Signup (synched_at)

If required information is missing from the response, stop signup according to your service policy, or provide a separate flow so that the user can enter the information directly on your service screen.

Your service server calls the Retrieve consent details for service terms API to check which service terms the user consented to.

Service terms are identified by the tag specified when configuring Simple Signup. Your service compares the required terms tags registered in the app with the user's consent details to determine whether signup can be completed.

For users who have not consented to the required terms, handle them in one of the following ways.

• Request consent again only for the required terms using the Get consent to desired service terms API
• Process additional consent on your service's own terms consent screen

Even if a user consents to add a Kakao Talk Channel on the Kakao Sync Consent screen, if your service needs to provide benefits or manage message recipients based on the user's Kakao Talk Channel friend status, use the Check Kakao Talk Channel relationship API.

Channel friend status is separate from the connection status between your service app and the user. Even if a user unlinks from your service app, the Kakao Talk Channel friend status may remain.

After checking user information and service terms consent details, your service performs signup or login processing in the service database.

• New user: If there is no matching service member, store the Kakao service user ID and required user information, then create a service member.
• Existing member: According to your service policy, find the existing service member, and map and store that member with the Kakao member ID after obtaining the user's consent.
• Already linked user: Find the member by the Kakao service user ID stored in the service database and process login.

For details, see Kakao Login > Mapping.

Completing Kakao Login or Kakao Sync consent does not automatically complete login for your service.

After your service creates a new member or finds an existing member, you must create a service session so that the user can use the service while logged in, then navigate to the login completion screen.

To use Kakao Sync, the following settings must be completed in your app. For the overall setup process, see Prerequisites.

• Activate Kakao Login
• Redirect URI
• Consent items
• Simple Signup

Before starting Kakao Sync development, first design which screens and processing steps the user goes through after the Kakao Sync Consent screen to complete service signup or login.

Kakao Sync obtains the consent required for signup on the Consent screen and lets your service retrieve user information and service terms consent details. Your service itself must implement member registration, existing member verification, account linking, and additional information collection.

We recommend a basic flow that completes signup right after the Kakao Sync Consent screen, with as little additional input as possible.

1. The user selects the [Start with Kakao] button.
2. On the Kakao Login Consent screen, the user consents to user information provision and service terms.
3. Your service checks the information and service terms consent status required for signup using Retrieve user information and Retrieve consent details for service terms.
4. Your service checks whether the user is an existing member in the service database.
5. If the user is new, register the user as a service member. If the user is an existing member, link the existing member with the Kakao service user ID after obtaining the user's consent.
6. Issue a service session and complete login processing.

If your service is already live, a user who signs in with Kakao Sync may already be an existing member. First check whether the user is an existing member, then provide the appropriate flow (new signup or existing member linking) based on the result.

Use the following priority when checking for an existing member.

When linking with an existing member, always confirm whether the user wants to link accounts. Even if information matches, the actual account owner may differ, or the user may want to sign up with a new account. For detailed processing flows, see Member registration and Mapping.

Even for consent items set as [Required consent], values may be missing from the Retrieve user information response. [Required consent] means the user must consent to providing the information to continue signup. It does not mean Kakao creates and provides a value that does not exist in the Kakao Account.

If required information for service signup is missing from the Retrieve user information response, your service must provide a separate flow according to its policy.

• Provide an additional input screen so the user can enter the information directly.
• If identity verification is required, implement and provide your own identity verification process.
• Inform the user that signup cannot proceed without the required information, then stop signup.

Here are the typical cases where your service cannot receive user information and the recommended actions.

For provision conditions by user information item, see User information. For detailed causes and solutions, see FAQ.

Integrate APIs by referring to Kakao Sync Simple Signup process.

For platform-specific API development documents, see the following.

• REST API
• JavaScript SDK
• Android SDK
• iOS SDK
• Flutter SDK

After completing integration development, finally check the following items before applying Kakao Sync to the production service.

After development is complete, verify the following scenarios with actual accounts.

See each related document for detailed configuration methods.

When you need to send users directly to the Kakao Sync Consent screen from an offline QR code or Kakao Bizboard Ad View as described in Marketing, you must additionally develop a landing page.

If you need to create a Kakao Sync permalink for QR codes, see Request a Kakao Sync permalink.

For a service that implements Kakao Login with a REST API key, enter a service URL that starts the Kakao Login authorization code request as the landing URL of the QR code or Ad View button. This is usually the URL called by your service's [Start with Kakao] button.

https://a.com/login/kakao

If it is difficult to provide a separate service login URL, you can use a Kakao Login authorization code request URL that starts with https://kauth.kakao.com/oauth/authorize. In this case, pass the REST API key in client_id, and pass the same value as the Redirect URI registered in the app in redirect_uri.

https://kauth.kakao.com/oauth/authorize?client_id=${REST_API_KEY}&redirect_uri=${REDIRECT_URI}&response_type=code

If you need to distinguish entry paths by store, campaign, or ad creative, you can include a tracking value in the state parameter of Request authorization code. Because state is also used to prevent CSRF, verify that the value issued by your service matches the value returned in the response.

For a service that implements Kakao Login with the JavaScript SDK, initialize the JavaScript SDK on the landing URL of the QR code or Ad View button, then call Kakao Login to open the Kakao Sync Consent screen.

For a better user experience, we recommend calling the Kakao Sync Consent screen immediately from a blank landing page.

Kakao.init("${JAVASCRIPT_KEY}")
Kakao.Auth.authorize({
  redirectUri: "${REDIRECT_URI}",
})

If you want to call the Consent screen automatically only in the Kakao Talk in-app browser, you can branch by checking the user agent.

Kakao.init("${JAVASCRIPT_KEY}")

if (/KAKAOTALK/i.test(navigator.userAgent)) {
  Kakao.Auth.authorize({
    redirectUri: "${REDIRECT_URI}",
  })
}