Problems with /api/3/user/assignable/search

I am trying to use the /api/3/user/assignable/search API from a my application server to disambiguate assignees when assigning an issue, and I see 2 problems:

  1. I am unable to get an exact match, e.g. if I issue /api/3/user/assignable/search?issueKey=SOME&query=First+Last, I seem to get all matches for First. Is there a way to get the exact match (assuming there’s only one matching result)
  2. To disambiguate multiple results, I need to access the EmailAddress (and Key?) of each returned user, but they are not filled in. I use user-impersonation OAuth2 with an atlassian-connect installed remote application.
    Note that invoking the same API URL from my browser where I am signed in as the same user returns the complete results.

Interestingly, when I invoke from the browser, signed in - I get the full JSON for the user, including the email.

When I do it from a (golang) server, using Atlassian Connect user impersonation, I get a sanitized version where the email is not set.

Apps, even when using user impersonation, are restricted to public information about users. If a user’s privacy setting restricts their email address, apps will not be able to access that information.

Please refer to
(see Personal Data Visibility Semantics section)