DoH query values that can be passed on the command line for testing
with curl can be obtained by encoding binary DNS messages into
base64url, with trailing '='s removed.
For example:
$ perl bin/tests/system/fromhex.pl << EOF | base64url
# Transaction ID
0001
# Standard query
0000
# Questions: 1, Additional: 0
0001 0000 0000 0000
# QNAME: example
07 6578616d706c65 00
# Type: SOA
0006
Class: IN
0001
EOF
This produces the string "AAEAAAABAAAAAAAAB2V4YW1wbGUAAAbFrMonAAE=". With
the trailing '=' removed, this can then be passed to curl:
curl "https://<server>/dns-query?dns=AAEAAAABAAAAAAAAB2V4YW1wbGUAAAbFrMonAAE"