Add support for the oauth2.el library in nnimap and smtpmail

* doc/misc/gnus.texi (Customizing the IMAP Connection):
* doc/misc/smtpmail.texi (Authentication): Mention it.

* lisp/gnus/nnimap.el (nnimap-login): Support oauth2.

* lisp/mail/smtpmail.el (smtpmail-try-auth-method): New function
for oauth2.

2 files changed, 15 insertions, 0 deletions

diff --git a/lisp/gnus/nnimap.el b/lisp/gnus/nnimap.el
index 3e2a202a6cf..3cf65453f3b 100644
--- a/lisp/gnus/nnimap.el
+++ b/lisp/gnus/nnimap.el
@@ -599,6 +599,13 @@ during splitting, which may be slow."
              (eq nnimap-authenticator 'anonymous)
 	     (eq nnimap-authenticator 'login)))
     (nnimap-command "LOGIN %S %S" user password))
+   ((and (nnimap-capability "AUTH=XOAUTH2")
+         (eq nnimap-authenticator 'xoauth2))
+    (nnimap-command  "AUTHENTICATE XOAUTH2 %s"
+                     (base64-encode-string
+                      (format "user=%s\001auth=Bearer %s\001\001"
+                              (nnimap-quote-specials user)
+                              (nnimap-quote-specials password)))))
    ((and (nnimap-capability "AUTH=CRAM-MD5")
 	 (or (null nnimap-authenticator)
 	     (eq nnimap-authenticator 'cram-md5)))
diff --git a/lisp/mail/smtpmail.el b/lisp/mail/smtpmail.el
index 33bdd050bdc..8e3927cdcf2 100644
--- a/lisp/mail/smtpmail.el
+++ b/lisp/mail/smtpmail.el
@@ -636,6 +636,14 @@ USER and PASSWORD should be non-nil."
 	   (base64-encode-string (concat "\0" user "\0" password) t))
    235))
 
+(cl-defmethod smtpmail-try-auth-method
+  (process (_mech (eql xoauth2)) user password)
+  (smtpmail-command-or-throw
+   process
+   (concat "AUTH XOAUTH2 "
+           (base64-encode-string
+            (concat "user=" user "\1auth=Bearer " password "\1\1") t))))
+
 (defun smtpmail-response-code (string)
   (when string
     (with-temp-buffer