(cloned from https://github.com/SSSD/sssd/issues/5568)

As discussed at https://lists.fedorahosted.org/archives/list/sssd-users@lists.fedorahosted.org/thread/GP3WO4WG54BCXLMI277MSLV5I5LFQU2G/ - when I try to use pam_sss_gss.so, it fails:
```
pam_sss_gss: Initializing GSSAPI authentication with SSSD
pam_sss_gss: Switching euid from 0 to 123456789
pam_sss_gss: Trying to establish security context
pam_sss_gss: SSSD User name: ...@example.net
pam_sss_gss: User domain: example.net
pam_sss_gss: User principal: ...@EXAMPLE.NET
pam_sss_gss: Target name: host.example.net
pam_sss_gss: Using ccache: FILE:/run/user/123456789/krb5cc
pam_sss_gss: Acquiring credentials for principal [...@EXAMPLE.NET]
pam_sss_gss: Communication error [3, 32]: Error in service module; Broken pipe
```

At the same time, sssd_pam logs:
```
(2021-04-01 10:55:00): [pam] [client_recv] (0x0400): Invalid data from client, closing connection!
```

The user is an AD user.

It looks like sssd_pam closes down the connection in `client_recv()` because `sss_packet_recv()` returns EINVAL, which it does if the request from the client is too large.

Maybe that's happening because the service ticket for host/myself.ipa.example.com is too large as it contains the PAC or whatever; using strace I can see the SSS_GSSAPI_SEC_CTX message being sent by the client is 1905 bytes long, but I think sssd_pam rejects requests larger than 1024 bytes (it reads the request into a 1536-byte buffer and then closes the connection rather than reading the rest).