Need guidance on retrieving existing GL user along with user role in OTM using any standard API

Summary:

We are currently developing an integration to update user roles (temporary role mapping) in OTM through an XML message from OIC.
As part of this requirement, first we need to retrieve the existing user role from OTM and store that information in an OIC staging table. This will allow us to restore the original role once the temporary role expires.
However, we could not find any standard API in OTM to retrieve the existing user role information.
Could you please advise if there is any standard or recommended approach to fetch user role details for a specific user from OTM for integration purposes?