pgsql: libpq: Trace frontend authentication challenges

libpq: Trace frontend authentication challenges

If tracing was enabled during connection startup, these messages would
previously be listed in the trace output as something like this:

F 54 Unknown message: 70
mismatched message length: consumed 4, expected 54

With this commit their type and contents are now correctly listed:

F 36 StartupMessage 3 0 "user" "foo" "database" "alvherre"
F 54 SASLInitialResponse "SCRAM-SHA-256" 32 'n,,n=,r=nq5zEPR/VREHEpOAZzH8Rujm'
F 108 SASLResponse 'c=biws,r=nq5zEPR/VREHEpOAZzH8RujmVtWZDQ8glcrvy9OMNw7ZqFUn,p=BBwAKe0WjSvigB6RsmmArAC+hwucLeuwJrR5C/HQD5M='

Author: Jelte Fennema-Nio <postgres(at)jeltef(dot)nl>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/CAGECzQSoPHtZ4xe0raJ6FYSEiPPS+YWXBhOGo+Y1YecLgknF3g@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ea92f3a0a5ad756600d94078a5d629c072ff61dd

Modified Files
--------------
src/interfaces/libpq/fe-auth.c | 6 ++++
src/interfaces/libpq/fe-trace.c | 69 ++++++++++++++++++++++++++++++++++++++++
src/interfaces/libpq/libpq-int.h | 16 +++++++++-
3 files changed, 90 insertions(+), 1 deletion(-)