Description of problem:
When using mod_auth_gssapi with Negotiate, GssapiLocalName and gssproxy, authentication fails.

Version-Release number of selected component (if applicable):
mod_auth_gssapi 1.6.1-6.el8
gssproxy 0.8.0-14.el8

How reproducible:
always

Steps to Reproduce:

1. Set up gssproxy, with configuration like this:

[service/HTTP]
  mechs = krb5
  cred_store = keytab:/etc/krb5.keytab
  cred_store = ccache:/var/lib/gssproxy/clients/krb5cc_%U
  euid = 48
  krb5_principal = HTTP

2. Set up httpd and mod_auth_gssapi, with configuration like this:

        AuthType GSSAPI
        AuthName "Login"
        GssapiCredStore keytab:/etc/krb5.keytab
        GssapiLocalName On
        GssapiBasicAuth On
        Require valid-user

3. Create /etc/systemd/system/httpd.service with this content:

.include /usr/lib/systemd/system/httpd.service
[Service]
Environment=GSS_USE_PROXY=1

4. Try to connect with a browser with Negotiate authentication

Actual results:
I get a 401 error, and a message like this appears in error_log:
[Fri Jan 03 12:35:22.497355 2020] [auth_gssapi:error] [pid xxx:xxx] [client xxx:xxx] GSS ERROR gss_localname() failed: [A required input parameter could not be read (Unknown error)]

Expected results:
I expect authentication to succeed.

Additional info:
This problem only occurs because all of gssproxy, GssapiLocalName, and Negotiate authentication are in use. If I do any one of the following, then it will work:

1. Unset GSS_USE_PROXY, and give Apache permission to read the keytab directly
2. Set "GssapiLocalName Off"
3. Connect with HTTP Basic authentication

Also, it's unrelated to SELinux, as it happens even with it in permissive mode.