Merge branch 'ag/imap-send-resurrection' into seen

"git imap-send" has been broken for a long time, which has been
resurrected and then taught to talk OAuth2.0 etc.

Ready?

* ag/imap-send-resurrection:
  imap-send: fix minor mistakes in the logs
  imap-send: display the destination mailbox when sending a message
  imap-send: display port alongwith host when git credential is invoked
  imap-send: add ability to list the available folders
  imap-send: enable specifying the folder using the command line
  imap-send: add PLAIN authentication method to OpenSSL
  imap-send: add support for OAuth2.0 authentication
  imap-send: gracefully fail if CRAM-MD5 authentication is requested without OpenSSL
  imap-send: fix memory leak in case auth_cram_md5 fails
  imap-send: fix bug causing cfg->folder being set to NULL

Author: gitster

Documentation/config/imap.adoc

@@ -1,7 +1,9 @@
 imap.folder::
 	The folder to drop the mails into, which is typically the Drafts
-	folder. For example: "INBOX.Drafts", "INBOX/Drafts" or
-	"[Gmail]/Drafts". Required.
+	folder. For example: `INBOX.Drafts`, `INBOX/Drafts` or
+	`[Gmail]/Drafts`. The IMAP folder to interact with MUST be specified;
+	the value of this configuration variable is used as the fallback
+	default value when the `--folder` option is not given.
 
 imap.tunnel::
 	Command used to set up a tunnel to the IMAP server through which
@@ -40,5 +42,6 @@ imap.authMethod::
 	Specify the authentication method for authenticating with the IMAP server.
 	If Git was built with the NO_CURL option, or if your curl version is older
 	than 7.34.0, or if you're running git-imap-send with the `--no-curl`
-	option, the only supported method is 'CRAM-MD5'. If this is not set
-	then 'git imap-send' uses the basic IMAP plaintext LOGIN command.
+	option, the only supported methods are `PLAIN`, `CRAM-MD5`, `OAUTHBEARER`
+	and `XOAUTH2`. If this is not set then `git imap-send` uses the basic IMAP
+	plaintext `LOGIN` command.

Documentation/git-imap-send.adoc

@@ -9,21 +9,24 @@ git-imap-send - Send a collection of patches from stdin to an IMAP folder
 SYNOPSIS
 --------
 [verse]
-'git imap-send' [-v] [-q] [--[no-]curl]
+'git imap-send' [-v] [-q] [--[no-]curl] [(--folder|-f) <folder>]
+'git imap-send' --list
 
 
 DESCRIPTION
 -----------
-This command uploads a mailbox generated with 'git format-patch'
+This command uploads a mailbox generated with `git format-patch`
 into an IMAP drafts folder.  This allows patches to be sent as
 other email is when using mail clients that cannot read mailbox
 files directly. The command also works with any general mailbox
-in which emails have the fields "From", "Date", and "Subject" in
+in which emails have the fields `From`, `Date`, and `Subject` in
 that order.
 
 Typical usage is something like:
 
-git format-patch --signoff --stdout --attach origin | git imap-send
+------
+$ git format-patch --signoff --stdout --attach origin | git imap-send
+------
 
 
 OPTIONS
@@ -37,6 +40,11 @@ OPTIONS
 --quiet::
 	Be quiet.
 
+-f <folder>::
+--folder=<folder>::
+	Specify the folder in which the emails have to saved.
+	For example: `--folder=[Gmail]/Drafts` or `-f INBOX/Drafts`.
+
 --curl::
 	Use libcurl to communicate with the IMAP server, unless tunneling
 	into it.  Ignored if Git was built without the USE_CURL_FOR_IMAP_SEND
@@ -47,6 +55,8 @@ OPTIONS
 	using libcurl.  Ignored if Git was built with the NO_OPENSSL option
 	set.
 
+--list::
+	Run the IMAP LIST command to output a list of all the folders present.
 
 CONFIGURATION
 -------------
@@ -102,20 +112,56 @@ Using Gmail's IMAP interface:
 
 ---------
 [imap]
-	folder = "[Gmail]/Drafts"
-	host = imaps://imap.gmail.com
-	user = [email protected]
-	port = 993
+    folder = "[Gmail]/Drafts"
+    host = imaps://imap.gmail.com
+    user = [email protected]
+    port = 993
 ---------
 
+Gmail does not allow using your regular password for `git imap-send`.
+If you have multi-factor authentication set up on your Gmail account, you
+can generate an app-specific password for use with `git imap-send`.
+Visit https://security.google.com/settings/security/apppasswords to create
+it. Alternatively, use OAuth2.0 authentication as described below.
+
 [NOTE]
 You might need to instead use: `folder = "[Google Mail]/Drafts"` if you get an error
-that the "Folder doesn't exist".
+that the "Folder doesn't exist". You can also run `git imap-send --list` to get a
+list of available folders.
 
 [NOTE]
 If your Gmail account is set to another language than English, the name of the "Drafts"
 folder will be localized.
 
+If you want to use OAuth2.0 based authentication, you can specify
+`OAUTHBEARER` or `XOAUTH2` mechanism in your config. It is more secure
+than using app-specific passwords, and also does not enforce the need of
+having multi-factor authentication. You will have to use an OAuth2.0
+access token in place of your password when using this authentication.
+
+---------
+[imap]
+    folder = "[Gmail]/Drafts"
+    host = imaps://imap.gmail.com
+    user = [email protected]
+    port = 993
+    authmethod = OAUTHBEARER
+---------
+
+Using Outlook's IMAP interface:
+
+Unlike Gmail, Outlook only supports OAuth2.0 based authentication. Also, it
+supports only `XOAUTH2` as the mechanism.
+
+---------
+[imap]
+    folder = "Drafts"
+    host = imaps://outlook.office365.com
+    user = [email protected]
+    port = 993
+    authmethod = XOAUTH2
+---------
+
 Once the commits are ready to be sent, run the following command:
 
   $ git format-patch --cover-letter -M --stdout origin/master | git imap-send
@@ -124,6 +170,10 @@ Just make sure to disable line wrapping in the email client (Gmail's web
 interface will wrap lines no matter what, so you need to use a real
 IMAP client).
 
+In case you are using OAuth2.0 authentication, it is easier to use credential
+helpers to generate tokens. Credential helpers suggested in
+linkgit:git-send-email[1] can be used for `git imap-send` as well.
+
 CAUTION
 -------
 It is still your responsibility to make sure that the email message