By default, Okta OIDC applications populate the preferred_username claim in the ID token with the user's primary email address (userName), which may not meet requirements when an application expects a custom username format. This issue is resolved by updating the application's attribute mappings in the Okta Profile Editor to map the desired profile attribute or custom Okta Expression Language value.

• OpenID Connect (OIDC) 
• Okta Identity Engine (OIE)
• Okta Classic Engine
• Profile Editor & Attribute Mapping

What requirements are needed for changing the Username of an OIDC Application?

• 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 attributes from the Claim?

1. Log in to the Okta Admin Console.
2. Navigate to Directory > Profile Editor.
3. Select Apps and locate the OIDC application.
4. Click Mappings.
5. In the profile mappings section, modify the following:
6. Click Save Mappings and apply changes to existing users if prompted.

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 
• Okta Expression Language Overview
• Customize Claims with Custom Authorization Servers
• OAuth 2.0 Scopes