Added get_real_instance_domain.

A script for finding out the real IP of an instance.

get_real_instance_domain.sh

@@ -0,0 +1,30 @@
+#!/bin/sh
+# Triggers an HTTPS connection from the remote Fediverse instance to your host.
+# Works only if the remote instance checks signatures. You need an HTTPS server
+# running on <Your host> with access logging activated in order for this to
+# work.
+
+# Version: 2019-08-17_1
+
+if [ -z "${2}" ]; then
+    echo "Usage: ${0} <Your host> <Remote host> [additional curl options]" >&2
+    exit 1
+fi
+
+your_host="${1}"
+remote_host="${2}"
+
+if command -v md5sum > /dev/null; then
+    uuid="$(date | md5sum | cut -d' ' -f 1)"
+else
+    echo "Warning: md5sum not found." >&2
+    uuid="4c2896dcba1597e2768387bc1e0e727a"
+fi
+
+sig='Signature: keyId="https://'"${your_host}/${uuid}"'",algorithm="rsa-sha256"'
+sig="${sig}"',headers="(request-target) host date content-type",signature="Aa="'
+
+curl -H "${sig}" -H "Date: $(date -Ru|sed -e 's/+0000/GMT/')" \
+     -H "Content-Type: application/activity+json" -d '{}' "${@}" \
+     "https://${remote_host}/inbox"
+echo