set the default value of SMTP_AUTHENTICATION to ':login' if SMTP_USER is set

Author: Sameer Naik

README.md

@@ -423,7 +423,7 @@ The following environment variables need to be specified to get mail support to
 * SMTP_USER
 * SMTP_PASS
 * SMTP_STARTTLS (defaults to true)
-* SMTP_AUTHENTICATION (defaults to :login)
+* SMTP_AUTHENTICATION (defaults to :login if SMTP_USER is set)
 
 ```bash
 docker run --name=gitlab -d \
@@ -603,7 +603,7 @@ Below is the complete list of available options that can be used to customize yo
 - **SMTP_USER**: SMTP username.
 - **SMTP_PASS**: SMTP password.
 - **SMTP_STARTTLS**: Enable STARTTLS. Defaults to true.
-- **SMTP_AUTHENTICATION**: Specify the SMTP authentication method. Defaults to :login.
+- **SMTP_AUTHENTICATION**: Specify the SMTP authentication method. Defaults to :login if SMTP_USER is set.
 - **LDAP_ENABLED**: Enable LDAP. Defaults to false
 - **LDAP_HOST**: LDAP Host
 - **LDAP_PORT**: LDAP Port. Defaults to 636

assets/init

@@ -45,7 +45,8 @@ SMTP_PORT=${SMTP_PORT:-587}
 SMTP_USER=${SMTP_USER:-}
 SMTP_PASS=${SMTP_PASS:-}
 SMTP_STARTTLS=${SMTP_STARTTLS:-true}
-SMTP_AUTHENTICATION=${SMTP_AUTHENTICATION:-:login}
+[ -n "${SMTP_USER}" ] && \
+	SMTP_AUTHENTICATION=${SMTP_AUTHENTICATION:-:login}
 
 LDAP_ENABLED=${LDAP_ENABLED:-false}
 LDAP_HOST=${LDAP_HOST:-}
@@ -344,11 +345,11 @@ esac
 
 sudo -u git -H sed 's/{{SMTP_DOMAIN}}/'"${SMTP_DOMAIN}"'/' -i /home/git/gitlab/config/initializers/smtp_settings.rb
 sudo -u git -H sed 's/{{SMTP_STARTTLS}}/'"${SMTP_STARTTLS}"'/' -i /home/git/gitlab/config/initializers/smtp_settings.rb
-if [ -n "${SMTP_AUTHENTICATION}" ]; then
-	sudo -u git -H sed '/{{SMTP_AUTHENTICATION}}/d' -i /home/git/gitlab/config/initializers/smtp_settings.rb
-else
-	sudo -u git -H sed 's/{{SMTP_AUTHENTICATION}}/'"${SMTP_AUTHENTICATION}"'/' -i /home/git/gitlab/config/initializers/smtp_settings.rb
-fi
+
+case "${SMTP_AUTHENTICATION}" in
+	"") sudo -u git -H sed '/{{SMTP_AUTHENTICATION}}/d' -i /home/git/gitlab/config/initializers/smtp_settings.rb ;;
+	*) sudo -u git -H sed 's/{{SMTP_AUTHENTICATION}}/'"${SMTP_AUTHENTICATION}"'/' -i /home/git/gitlab/config/initializers/smtp_settings.rb ;;
+esac
 
 # apply LDAP configuration
 sudo -u git -H sed 's/{{LDAP_ENABLED}}/'"${LDAP_ENABLED}"'/' -i /home/git/gitlab/config/gitlab.yml