When castellan trying to recreate trust-scoped token
from RequestContext keystone throw exception
because it's not allowed.
Starting from this commit castellan trying to
reuse existing token constructed from RequestContext
if get_auth_plugin() is available.
Change-Id: I10a12b9a2a7f796eca37dd20a280d3a4015a6903
Closes-Bug: #1827047
Depends-On: https://review.opendev.org/#/c/664558/
(cherry picked from commit 5d93676338)
193b4a2cc3