Noticed this while I was in the area. We currently use an extremely lax
parse that even tolerates syntax errors. Instead use a strict parse that
ensures our client only sends what we expect.
Change-Id: Ifb0e1e1698489ff217db0c7a0317caa885e20759
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/47966
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>