GUACAMOLE-626: Add Docker secret support for MySQL and Postgres

Add support for reading from docker secret files. New script prefers environment variables ending with _FILE over normal variables, meaning that Docker secrets will take precedence. You can, however, mix variable types, ex. MYSQL_USER uses a normal environment variable, while MYSQL_PASSWORD uses a secret.

guacamole-docker/bin/start.sh

@@ -125,13 +125,13 @@ END
         exit 1;
     fi
 
-    # Verify required parameters are present
+    MYSQL_MISSING_VARS=`cat <<END
-    if [ -z "$MYSQL_USER" -o -z "$MYSQL_PASSWORD" -o -z "$MYSQL_DATABASE" ]; then
-        cat <<END
 FATAL: Missing required environment variables
 -------------------------------------------------------------------------------
 If using a MySQL database, you must provide each of the following
-environment variables:
+environment variables or their corresponding Docker secrets by appending _FILE
+to the environment variable, and setting the value to the path of the 
+corresponding secret:
 
     MYSQL_USER         The user to authenticate as when connecting to
                        MySQL.
@@ -141,16 +141,39 @@ environment variables:
 
     MYSQL_DATABASE     The name of the MySQL database to use for Guacamole
                        authentication.
-END
+END`
+
+    # Verify that the required Docker secrets are present, else, default to their normal environment variables
+    if [ -n "$MYSQL_USER_FILE" ]; then
+        set_property "mysql-username" `cat $MYSQL_USER_FILE`
+    elif [ -n "$MYSQL_USER" ]; then
+        set_property "mysql-username" "$MYSQL_USER"
+    else
+        cat "$MYSQL_MISSING_VARS"
+        exit 1;
+    fi
+    
+    if [ -n "$MYSQL_PASSWORD_FILE" ]; then
+        set_property "mysql-password" `cat $MYSQL_PASSWORD_FILE`
+    elif [ -n "$MYSQL_PASSWORD" ]; then
+        set_property "mysql-password" "$MYSQL_PASSWORD"
+    else
+        cat "$MYSQL_MISSING_VARS"
+        exit 1;
+    fi
+
+    if [ -n "$MYSQL_DATABASE_FILE" ]; then
+        set_property "mysql-database" `cat $MYSQL_DATABASE_FILE`
+    elif [ -n "$MYSQL_DATABASE" ]; then
+        set_property "mysql-database" "$MYSQL_DATABASE"
+    else
+        cat "$MYSQL_MISSING_VARS"
         exit 1;
     fi
 
     # Update config file
     set_property "mysql-hostname" "$MYSQL_HOSTNAME"
     set_property "mysql-port"     "$MYSQL_PORT"
-    set_property "mysql-database" "$MYSQL_DATABASE"
-    set_property "mysql-username" "$MYSQL_USER"
-    set_property "mysql-password" "$MYSQL_PASSWORD"
 
     set_optional_property               \
         "mysql-absolute-max-connections" \
@@ -221,13 +244,13 @@ END
         exit 1;
     fi
 
-    # Verify required parameters are present
+    POSTGRES_MISSING_VARS=`cat <<END
-    if [ -z "$POSTGRES_USER" -o -z "$POSTGRES_PASSWORD" -o -z "$POSTGRES_DATABASE" ]; then
-        cat <<END
 FATAL: Missing required environment variables
 -------------------------------------------------------------------------------
 If using a PostgreSQL database, you must provide each of the following
-environment variables:
+environment variables or their corresponding Docker secrets by appending _FILE
+to the environment variable, and setting the value to the path of the 
+corresponding secret:
 
     POSTGRES_USER      The user to authenticate as when connecting to
                        PostgreSQL.
@@ -237,16 +260,45 @@ environment variables:
 
     POSTGRES_DATABASE  The name of the PostgreSQL database to use for Guacamole
                        authentication.
-END
+END`
+
+    # Verify that the required Docker secrets are present, else, default to their normal environment variables
+    if [ -n "$POSTGRES_USER_FILE" ]; then
+        set_property "postgresql-username" `cat $POSTGRES_USER_FILE`
+    elif [ -n "$POSTGRES_USER" ]; then
+        set_property "postgresql-username" "$POSTGRES_USER"
+    else
+        cat "$POSTGRES_MISSING_VARS"
+        exit 1;
+    fi
+    
+    if [ -n "$POSTGRES_PASSWORD_FILE" ]; then
+        set_property "postgresql-password" `cat $POSTGRES_PASSWORD_FILE`
+    elif [ -n "$POSTGRES_PASSWORD" ]; then
+        set_property "postgresql-password" "$POSTGRES_PASSWORD"
+    else
+        cat "$POSTGRES_MISSING_VARS"
+        exit 1;
+    fi
+
+    if [ -n "$POSTGRES_DATABASE_FILE" ]; then
+        set_property "postgresql-database" `cat $POSTGRES_DATABASE_FILE`
+    elif [ -n "$POSTGRES_DATABASE" ]; then
+        set_property "postgresql-database" "$POSTGRES_DATABASE"
+    else
+        cat "$POSTGRES_MISSING_VARS"
+        exit 1;
+    fi
+
+    # Verify required parameters are present
+    if [ -z "$POSTGRES_USER" -o -z "$POSTGRES_PASSWORD" -o -z "$POSTGRES_DATABASE" ]; then
+        cat 
         exit 1;
     fi
 
     # Update config file
     set_property "postgresql-hostname" "$POSTGRES_HOSTNAME"
     set_property "postgresql-port"     "$POSTGRES_PORT"
-    set_property "postgresql-database" "$POSTGRES_DATABASE"
-    set_property "postgresql-username" "$POSTGRES_USER"
-    set_property "postgresql-password" "$POSTGRES_PASSWORD"
 
     set_optional_property               \
         "postgresql-absolute-max-connections" \