Merge branch '10-add-the-ability-to-use-secrets-for-credentials' into 'master'

Resolve #10 "Add the ability to use secrets for credentials"

See merge request ix.ai/smtp!11

Author: tlex

entrypoint.sh

@@ -1,6 +1,36 @@
 #!/usr/bin/env bash
 set -e
 
+# usage: file_env VAR [DEFAULT]
+#    ie: file_env 'XYZ_DB_PASSWORD' 'example'
+# (will allow for "$XYZ_DB_PASSWORD_FILE" to fill in the value of
+#  "$XYZ_DB_PASSWORD" from a file, especially for Docker's secrets feature)
+file_env() {
+        local var="$1"
+        local fileVar="${var}_FILE"
+        local varName="${!var@}"
+        local def="${2:-}"
+        if [ "${!var:-}" ] && [ "${!fileVar:-}" ]; then
+                echo >&2 "error: both ${varName} and ${fileVar} are set (but are mutually exclusive)"
+                exit 1
+        fi
+        local val="$def"
+        if [ "${!var:-}" ]; then
+                val="${!var}"
+        elif [ "${!fileVar:-}" ]; then
+                val="$(< "${!fileVar}")"
+        fi
+        export "$var"="$val"
+        unset "$fileVar"
+}
+
+file_env GMAIL_USER
+file_env GMAIL_PASSWORD
+file_env SES_USER
+file_env SES_PASSWORD
+file_env SMARTHOST_USER
+file_env SMARTHOST_PASSWORD
+
 # Initialize localmacros as an empty file
 echo -n "" > /etc/exim4/exim4.conf.localmacros