send-email: add option to generate passswords like OAuth2 tokens

Some email providers like outlook allow only OAuth2 tokens to be used
for authentication. This commit adds an option to generate OAuth2 tokens
using scripts like M365-IMAP[1]. This option is similar to passwordeval
in msmtp.

Example usage:

[sendemail]
    smtpEncryption = tls
    smtpServer = smtp.office365.com
    smtpUser = [email protected]
    smtpServerPort = 587
    smtpauth = XOAUTH2
    smtpPassEval = cd /workspaces/codespaces-blank/M365-IMAP && python3 ./refresh_token.py

Signed-off-by: Aditya Garg <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: AdityaGarg8

Documentation/git-send-email.adoc

@@ -230,6 +230,14 @@ or on the command line. If a username has been specified (with
 specified (with `--smtp-pass` or `sendemail.smtpPass`), then
 a password is obtained using 'git-credential'.
 
+--smtp-passeval[=<command>]::
+	Generate password like OAuth2 token for SMTP AUTH. If specified,
+	it will use the output of the command specified as a password for
+	authentication.
++
+Note that it will override any existing password specified using
+`--smtp-pass` or a `sendemail.smtpPass`.
+
 --no-smtp-auth::
 	Disable SMTP authentication. Short hand for `--smtp-auth=none`
 

git-send-email.perl

@@ -59,6 +59,8 @@ sub usage {
     --smtp-server-port      <int>  * Outgoing SMTP server port.
     --smtp-user             <str>  * Username for SMTP-AUTH.
     --smtp-pass             <str>  * Password for SMTP-AUTH; not necessary.
+    --smtp-passeval         <str>  * Path to script or a command to generate
+                                     password like OAuth2 token for SMTP-AUTH.
     --smtp-encryption       <str>  * tls or ssl; anything else disables.
     --smtp-ssl                     * Deprecated. Use '--smtp-encryption ssl'.
     --smtp-ssl-cert-path    <str>  * Path to ca-certificates (either directory or file).
@@ -280,6 +282,7 @@ sub do_edit {
 my ($auto_8bit_encoding);
 my ($compose_encoding);
 my ($sendmail_cmd);
+my ($smtp_authpasseval);
 my ($mailmap_file, $mailmap_blob);
 # Variables with corresponding config settings & hardcoded defaults
 my ($debug_net_smtp) = 0;		# Net::SMTP, see send_message()
@@ -316,6 +319,7 @@ sub do_edit {
     "smtppass" => \$smtp_authpass,
     "smtpdomain" => \$smtp_domain,
     "smtpauth" => \$smtp_auth,
+    "smtppasseval" => \$smtp_authpasseval,
     "smtpbatchsize" => \$batch_size,
     "smtprelogindelay" => \$relogin_delay,
     "to" => \@config_to,
@@ -516,6 +520,7 @@ sub config_regexp {
 		    "smtp-server-port=s" => \$smtp_server_port,
 		    "smtp-user=s" => \$smtp_authuser,
 		    "smtp-pass:s" => \$smtp_authpass,
+		    "smtp-passeval=s" => \$smtp_authpasseval,
 		    "smtp-ssl" => sub { $smtp_encryption = 'ssl' },
 		    "smtp-encryption=s" => \$smtp_encryption,
 		    "smtp-ssl-cert-path=s" => \$smtp_ssl_cert_path,
@@ -1463,6 +1468,16 @@ sub smtp_auth_maybe {
 		return 1;
 	}
 
+	# If smtpPassEval is set, run the user specified command to get the password
+	if (defined $smtp_authpasseval) {
+		printf __("Executing token generating script: %s\n"), $smtp_authpasseval;
+		chomp(my $generated_password = `$smtp_authpasseval 2>&1`);
+		if ($? != 0) {
+			die sprintf(__("Failed to execute token generating script: %s\n"), $smtp_authpasseval);
+		}
+		$smtp_authpass = $generated_password;
+	}
+
 	# Workaround AUTH PLAIN/LOGIN interaction defect
 	# with Authen::SASL::Cyrus
 	eval {