The OTK Oauth Manager uses the default Internal Identity Provider for logging in to the UI:
This behavior can be customized in the 'OTK User Authentication Extension' policy.
All versions of the Oauth Tool Kit
1. Find the 'OTK User Authentication Extension' policy in the Policy Manager under the folder structure OTK --> Customizations --> authentication.
2. Locate the 'Request: Authenticate against Internal Identity Provider' assertion.
3. Double click this assertion to choose the provider of your choice based on your configured IDPs.
4. Save and activate the policy.
Now you should be able to login with admin users from your selected Identity Provider.