feat: add "gssapi-keyex" for server

feat: add negative auth client tests, and more key exchange server tests

feat: add function for checkinf if GSSAPI key exchange was performed
Signed-off-by: Gauravsingh Sisodia <xaerru@gmail.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/gssapi.h

@@ -89,6 +89,8 @@ OM_uint32 ssh_gssapi_init_ctx(struct ssh_gssapi_struct *gssapi,
 char *ssh_gssapi_oid_hash(ssh_string oid);
 char *ssh_gssapi_kex_mechs(ssh_session session, const char *gss_algs);
 int ssh_gssapi_check_client_config(ssh_session session);
+ssh_buffer ssh_gssapi_build_mic(ssh_session session, const char *context);
+int ssh_gssapi_auth_keyex_mic(ssh_session session, gss_buffer_desc *mic_token_buf);
 
 #ifdef __cplusplus
 }

include/libssh/kex.h

@@ -31,6 +31,8 @@ struct ssh_kex_struct {
     char *methods[SSH_KEX_METHODS];
 };
 
+#include "libssh/crypto.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -64,6 +66,7 @@ int ssh_make_sessionid(ssh_session session);
 int ssh_hashbufin_add_cookie(ssh_session session, unsigned char *cookie);
 int ssh_hashbufout_add_cookie(ssh_session session);
 int ssh_generate_session_keys(ssh_session session);
+bool ssh_kex_is_gss(struct ssh_crypto_struct *crypto);
 
 #ifdef __cplusplus
 }

include/libssh/server.h

@@ -247,6 +247,7 @@ LIBSSH_API void ssh_bind_free(ssh_bind ssh_bind_o);
  *                          SSH_AUTH_METHOD_HOSTBASED
  *                          SSH_AUTH_METHOD_INTERACTIVE
  *                          SSH_AUTH_METHOD_GSSAPI_MIC
+ *                          SSH_AUTH_METHOD_GSSAPI_KEYEX
  */
 LIBSSH_API void ssh_set_auth_methods(ssh_session session, int auth_methods);