Add support for authentication/STARTTLS to SMTP

Add support for user/password based authentication to the SMTP driver of
Zuul. It is now possible to use "user" and "password" as options for the
smtp driver plus "use_starttls" to encrypt the SMTP conenction.

In addition, this change also changes the way error handling is done in
the SMTP driver: A failed send attempt is now immediately reported in
the log as a warning and no error string is returned anymore since it
wasn't used on the call site.

Change-Id: I456f7a2b3e21cf72f68820064ab6acc72a369ba1

doc/source/admin/drivers/smtp.rst

@@ -40,6 +40,22 @@ Connection Configuration
       Who the report should be emailed to by default.
       This can be overridden by individual pipelines.
 
+   .. attr:: user
+
+      Optional user name used to authenticate to the SMTP server. Used only in
+      conjunction with a password. If no password is present, this option is
+      ignored.
+
+   .. attr:: password
+
+      Optional password used to authenticate to the SMTP server.
+
+   .. attr:: use_starttls
+      :default: false
+
+      Issue a STARTTLS request to establish an encrypted channel after having
+      connected to the SMTP server.
+
 Reporter Configuration
 ----------------------
 

zuul/driver/smtp/smtpconnection.py

@@ -36,6 +36,13 @@ class SMTPConnection(BaseConnection):
             'default_from', 'zuul')
         self.smtp_default_to = self.connection_config.get(
             'default_to', 'zuul')
+        self.smtp_user = self.connection_config.get('user')
+        self.smtp_pass = self.connection_config.get('password')
+        starttls = self.connection_config.get('use_starttls', 'false')
+        if starttls.lower() == 'false':
+            self.smtp_starttls = False
+        else:
+            self.smtp_starttls = True
 
     def sendMail(self, subject, message, from_email=None, to_email=None):
         # Create a text/plain email message
@@ -50,11 +57,15 @@ class SMTPConnection(BaseConnection):
 
         try:
             s = smtplib.SMTP(self.smtp_server, self.smtp_port)
+            if self.smtp_starttls:
+                s.starttls()
+                s.ehlo()
+            if self.smtp_user is not None and self.smtp_pass is not None:
+                s.login(self.smtp_user, self.smtp_pass)
             s.sendmail(from_email, to_email.split(','), msg.as_string())
             s.quit()
-        except Exception:
-            return "Could not send email via SMTP"
-        return
+        except Exception as e:
+            self.log.warning("Error sending mail via SMTP: %s", e)
 
 
 def getSchema():