Based on my understanding of your question/scenario description, you may try the following if your requirement fits - To limit access to specific GitHub users when using GitHub as the Identity Provider for your App Service app, you may leverage Azure Active Directory (Azure AD) to manage access to your app.
- Add users to Azure AD: In the Azure portal, go to your Azure AD tenant and click on "Users". Click on "New user" to add a new user to Azure AD. You may also invite existing GitHub users to join your Azure AD tenant.
- Assign users to the app: In the Azure portal, go to your Azure AD tenant and click on "Enterprise applications". (Click on the application you created). Click on "Users and groups" and then click on "Add user/group". Select the users or groups that you want to grant access to your app and click on "Select". Choose the appropriate role for the users or groups (e.g. "User" or "Contributor") and click on "Assign".
Ref:
Configure your App Service or Azure Functions app to use GitHub login
Quickstart: Add an enterprise application
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