Use new GSSAPI Credential Store API
This is the only thread safe way to pass in aribitrary values for all the bits
of environment we want to use when doing impersonation within gss-proxy.
Requires MIT version 1.12 for the client_keytab part to be operational.
Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Günther Deschner <gdeschner@redhat.com>