Weird enough because the API docs say about the base URL:
“Host: localhost:8080 BasePath: /auth Schemes: HTTP”.
And I found nowhere the end-point docs you posted.
Second point, when testing you URL with curl -X GET -i http://localhost:8080/auth/admin/realms/demo/users I got the 401 response:
HTTP/1.1 401 Unauthorized
X-XSS-Protection: 1; mode=block
X-Frame-Options: SAMEORIGIN
Referrer-Policy: no-referrer
Date: Wed, 16 Sep 2020 06:38:28 GMT
Connection: keep-alive
Strict-Transport-Security: max-age=31536000; includeSubDomains
X-Content-Type-Options: nosniff
Content-Type: application/json
Content-Length: 33
{"error":"HTTP 401 Unauthorized"}%