Issue Summary

In Bitbucket Data Center 7.18, HTTP access tokens were added for projects and repositories: https://confluence.atlassian.com/bitbucketserver/http-access-tokens-939515499.html

These access tokens are associated with a service user. However, the rate-limiting exemptions UI doesn't allow selecting service users. 

This is reproducible on Data Center: Yes

Steps to Reproduce

1. Enable rate limiting on the Bitbucket instance
2. Create a project or repository access token
3. Trigger numerous REST API calls using the token until it is rate-limited
4. Navigate to the Rate limiting page
5. View the list of rate-limited users
6. On the ... button, select Manage Exemptions and try to whitelist the service user (they are listed as access-token-user)

Expected Results

An exemption is added for the service user

Actual Results

An error is displayed when adding an exemption for the service user: Could not update exemption - Invalid settings entered

Workaround

Currently, there is no known workaround for this behavior. A workaround will be added here when available