Without explicit conversion to UTC() from Unix
time the zone information is lost, this leads
to XML marshallers marshaling the time into
a wrong format.
This PR fixes the compatibility issue with AWS STS
API by keeping Expiration format close to ISO8601
or RFC3339
Fixes#8041
This PR adds support for adding session policies
for further restrictions on STS credentials, useful
in situations when applications want to generate
creds for multiple interested parties with different
set of policy restrictions.
This session policy is not mandatory, but optional.
Fixes#7732
