[PATCH v4 3/3] send-email: add option to generate passswords like OAuth2 tokens

[Aditya Garg <gargaditya08@xxxxxxxx>]

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 = someone@xxxxxxxxxxx
    smtpServerPort = 587
    smtpauth = XOAUTH2
    smtpPassEval = cd /workspaces/codespaces-blank/M365-IMAP && python3 ./refresh_token.py

Signed-off-by: Aditya Garg <gargaditya08@xxxxxxxx>
---
 Documentation/git-send-email.adoc |  8 ++++++++
 git-send-email.perl               | 15 +++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/Documentation/git-send-email.adoc b/Documentation/git-send-email.adoc
index 1bf75c060d..f478559582 100644
--- a/Documentation/git-send-email.adoc
+++ b/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`
 
diff --git a/git-send-email.perl b/git-send-email.perl
index a18e978e22..cafb9aa43b 100755
--- a/git-send-email.perl
+++ b/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 {
-- 
2.49.0