Store login failure error messages in the transaction
This will propogate messages up from failed form authentication
so they are correctly displayed in a SAML2 transaction for a
user with an expired password, for example.
The message is wiped after retrieval to ensure that a stale
message won't be displayed in the future.
Signed-off-by: Rob Crittenden <firstname.lastname@example.org>
Reviewed-by: Patrick Uiterwijk <email@example.com>