The REST API endpoints /rest/api/2/group and /rest/api/2/group/members are not case sensitive, while /rest/api/2/group/user is case sensitive

Summary

The endpoints /rest/api/2/group and /rest/api/2/group/members are not case sensitive, while /rest/api/2/group/user is.

GETting https://INSTANCE.atlassian.net/rest/api/2/group?groupname=test  or https://zaansmeisje.atlassian.net/rest/api/2/group?groupname=TesT returns the same results.

Environment

JIRA 1000.670.2

Steps to Reproduce

1. Create a group named TesT using the rest api
2. GET the group details and members by calling below endpoints, see that all of them works fine:
   • https://INSTANCE.atlassian.net/rest/api/2/group?groupname=TesT
   • https://INSTANCE.atlassian.net/rest/api/2/group?groupname=Test
   • https://INSTANCE.atlassian.net/rest/api/2/group?groupname=test
   • https://INSTANCE.atlassian.net/rest/api/2/group/members?groupname=test
   • https://INSTANCE.atlassian.net/rest/api/2/group/members?groupname=tESt
3. Now try to add or remove a user to the group without paying attention to the cases (e.g. using endpoint https://INSTANCE.atlassian.net/rest/api/2/group?groupname=test)

Expected Results

The user is added or removed to/from the group

Actual Results

You get the below error message:

{
  "errorMessages": [
    "You cannot add users to groups which are not visible to you."
  ],
  "errors": {}
}  

Notes

Adding the group TesT or test through the UI creates the same group (and it doesn't warn you that a group with the same name already exists).
(Optional - If Necessary)

Workaround

Use case sensitive names.