[krbdev.mit.edu #8972] krb5_init_creds_step() can make synchronous TGS requests for FAST armor TGTs

Thu Dec 17 00:27:37 2020: Request 8972 was acted upon.
 Transaction: Ticket created by [email protected]
       Queue: krb5
     Subject: krb5_init_creds_step() can make synchronous TGS requests for FAST
 armor TGTs
       Owner: Nobody
  Requestors: [email protected]
      Status: new
 Ticket <URL: https://krbdev.mit.edu/rt/Ticket/Display.html?id=8972 >


get_in_tkt.c calls krb5int_fast_as_armor(), which calls fast_armor_ap_request()
if the DO_FAST flag is set. To get the armor TGT, fast_armor_ap_request() calls
krb5_get_credentials() with no special flags. Under ordinary circumstances,
this just fetches the client-realm TGT from the cache. However, after a realm
referral, krb5_get_credentials() may be asked to retrieve a TGT for another
realm, in which case it will make TGS requests.

This behavior is intentional, but it does not honor the stepwise contract of
krb5_init_creds_step() (which was implemented later than the FAST code).
Instead of using the sequential API, we should create a TGS state machine to be
referenced from the AS step machine, and step through it until it is complete.