Description of problem:

As per [1] GSI authentication is non-functional since GSI-OpenSSH 8.0p1 because the GSS key exchange functionality is broken for GSI since this version, the SHA1 based GSS group exchange functionality is still working, though. This was confirmed on x86_64 but should affaect all other architectures, too.

[1]: https://github.com/openssh-gsskex/openssh-gsskex/issues/18

Version-Release number of selected component (if applicable):

8.0p1-6.el8

How reproducible:

always

Steps to Reproduce:

Install [gsi-openssh-8.0p1-6.el8] server and clients. Configure `gsisshd` to listen on TCP port `2222`. Configure GSI (host cert and key, grid-mapfile) and create a GSI proxy certificate. Also install the test script from https://gist.github.com/fscheiner/92ea125c72cd70283a712585206c1015 which starts a `gsisshd` and tries to connect and authenticate via GSI to this GSI-OpenSSH server instance with `gsissh`.

[gsi-openssh-8.0p1-6.el8]: https://kojipkgs.fedoraproject.org//packages/gsi-openssh/8.0p1/6.el8/x86_64/

```
[johndoe@host ~]$ sudo bin/test-gss-kex-for-gsi-openssh.bash host.domain.tld johndoe2
```

Actual results:

Only GSS GEX method `gss-gex-sha1-` is working:

```
gsisshd: OpenSSH_8.0p1c-GSI GSI-hpn14v19, OpenSSL 1.1.1c FIPS  28 May 2019
gsissh: OpenSSH_8.0p1c-GSI GSI-hpn14v19, OpenSSL 1.1.1c FIPS  28 May 2019

Wait 3 seconds for startup of gsisshd ...

gss-gex-sha1- OK
gss-group1-sha1- Error
gss-group14-sha256- Error
gss-nistp256-sha256- Error
gss-curve25519-sha256- Error
gss-group16-sha512- Error

[johndoe@host ~]$ yum info gsi-openssh
[...]
Installed Packages
Name         : gsi-openssh
Version      : 8.0p1
Release      : 6.el8
Architecture : x86_64
Size         : 1.9 M
Source       : gsi-openssh-8.0p1-6.el8.src.rpm
[...]

```

Expected results:

All GSS KEX/GEX methods (`gss-group1-sha1-`,`gss-group14-sha1-`,`gss-group14-sha256-`,`gss-group16-sha512-`,`gss-nistp256-sha256-`,`gss-curve25519-sha256-`,`gss-gex-sha1-`) are working:

```
gsisshd: OpenSSH_8.0p1c-GSI GSI-hpn14v19, OpenSSL 1.1.1c FIPS  28 May 2019
gsissh: OpenSSH_8.0p1c-GSI GSI-hpn14v19, OpenSSL 1.1.1c FIPS  28 May 2019

Wait 3 seconds for startup of gsisshd ...

gss-gex-sha1- OK
gss-group1-sha1- OK
gss-group14-sha256- OK
gss-nistp256-sha256- OK
gss-curve25519-sha256- OK
gss-group16-sha512- OK
```

Additional info:

A fix based on [openssh-gsskex/openssh-gsskex#19] is available from here:

https://gist.github.com/fscheiner/ec430514b28e4dad24516c66939a8945

[openssh-gsskex/openssh-gsskex#19]: https://github.com/openssh-gsskex/openssh-gsskex/pull/19