This article details how to modify the preferred_username claim from the ID_token to a different value.

• OpenID Connect (OIDC)

General information and requirements:

• By default, the preferred_username claim is mapped as the "userName" in the application user profile, which will be populated as the primary email address of the user.
• In order to receive the preferred_username claim in the user's ID token, the profile scope must be included in the /authorize request (specified in the app code/service provider's configuration dashboard).

How to modify the claim

1. In the Okta Admin dashboard, navigate to Directory > Profile Editor. 
2. Select the Apps section.
3. Find the relevant OIDC app and select Mappings.
4. In the profile mappings section, modify the following:

The preferred_username claim can be modified to return a different value from the user's profile. (even a custom expression value can be used)

Related References

• ID Token payload
• Authorization request 
• OAuth 2.0 Scopes