None of the following functions are standard GSS API functions. As such, they are not declared in gss/api.h, but rather in gss/ext.h (which is included from gss.h). See Header.
const char * gss_check_version (const char * req_version) ¶req_version:
int gss_userok (const gss_name_t name, const char * username) ¶name: username: