dkim: Implement internal dkim signing and verification

This patch implements internal DKIM signing and verification.

test/t-21-dkim/run.sh

@@ -0,0 +1,67 @@
+#!/bin/bash
+
+set -e
+. "$(dirname "$0")/../util/lib.sh"
+
+init
+check_hostaliases
+
+rm -rf .data-A .data-B .mail
+
+skip_if_python_is_too_old
+
+# Build with the DNS override, so we can fake DNS records.
+export GOTAGS="dnsoverride"
+
+# srv-A has a pre-generated key, and the mail has a pre-generated header.
+# Generate a key for srv-B, and append it to our statically configured zones.
+# Use a fixed selector so we can be more thorough in from_B_to_A.expected.
+rm -f B/domains/srv-b/*.pem
+mkdir -p B/domains/srv-b/
+CONFDIR=B chasquid-util dkim-keygen srv-b sel77 --algo=ed25519 > /dev/null
+
+cp zones .zones
+CONFDIR=B chasquid-util dkim-dns srv-b | sed 's/"//g' >> .zones
+
+# Launch minidns in the background using our configuration.
+minidns_bg --addr=":9053" -zones=.zones >> .minidns.log 2>&1
+
+# Two servers:
+# A - listens on :1025, hosts srv-A
+# B - listens on :2015, hosts srv-B
+
+CONFDIR=A generate_certs_for srv-A
+CONFDIR=A add_user user-a@srv-a nadaA
+
+CONFDIR=B generate_certs_for srv-B
+CONFDIR=B add_user user-b@srv-b nadaB
+
+mkdir -p .logs-A .logs-B
+
+chasquid -v=2 --logfile=.logs-A/chasquid.log --config_dir=A \
+	--testing__dns_addr=127.0.0.1:9053 \
+	--testing__outgoing_smtp_port=2025 &
+chasquid -v=2 --logfile=.logs-B/chasquid.log --config_dir=B \
+	--testing__dns_addr=127.0.0.1:9053 \
+	--testing__outgoing_smtp_port=1025 &
+
+wait_until_ready 1025
+wait_until_ready 2025
+wait_until_ready 9053
+
+# Send from A to B.
+smtpc.py --server=localhost:1025 --user=user-a@srv-a --password=nadaA \
+	< from_A_to_B
+
+wait_for_file .mail/user-b@srv-b
+mail_diff from_A_to_B.expected .mail/user-b@srv-b
+
+# Send from B to A.
+smtpc.py --server=localhost:2025 --user=user-b@srv-b --password=nadaB \
+	< from_B_to_A
+
+wait_for_file .mail/user-a@srv-a
+mail_diff from_B_to_A.expected .mail/user-a@srv-a
+
+
+success