imap-login: Move forward_fields updating code to login-common

This allows using the new client_add_forward_field() in e.g. plugins.

src/imap-login/imap-login-client.c

@@ -7,7 +7,6 @@
 #include "ostream.h"
 #include "safe-memset.h"
 #include "str.h"
-#include "strescape.h"
 #include "imap-parser.h"
 #include "imap-id.h"
 #include "imap-resp-code.h"
@@ -188,15 +187,7 @@ client_update_info(struct imap_client *client,
 		}
 	} else if (strncasecmp(key, "x-forward-", 10) == 0) {
 		/* handle extra field */
-		if (client->common.forward_fields == NULL)
-			client->common.forward_fields = str_new(client->common.preproxy_pool, 32);
-		else
-			str_append_c(client->common.forward_fields, '\t');
-		/* prefixing is done by auth process */
-		str_append_tabescaped(client->common.forward_fields,
-				      key+10);
-		str_append_c(client->common.forward_fields, '=');
-		str_append_tabescaped(client->common.forward_fields, value);
+		client_add_forward_field(&client->common, key+10, value);
 	} else {
 		return FALSE;
 	}

src/login-common/client-common.c

@@ -11,6 +11,7 @@
 #include "hook-build.h"
 #include "buffer.h"
 #include "str.h"
+#include "strescape.h"
 #include "base64.h"
 #include "str-sanitize.h"
 #include "safe-memset.h"
@@ -488,6 +489,19 @@ unsigned int clients_get_count(void)
 	return clients_count;
 }
 
+void client_add_forward_field(struct client *client, const char *key,
+			      const char *value)
+{
+	if (client->forward_fields == NULL)
+		client->forward_fields = str_new(client->preproxy_pool, 32);
+	else
+		str_append_c(client->forward_fields, '\t');
+	/* prefixing is done by auth process */
+	str_append_tabescaped(client->forward_fields, key);
+	str_append_c(client->forward_fields, '=');
+	str_append_tabescaped(client->forward_fields, value);
+}
+
 const char *client_get_session_id(struct client *client)
 {
 	buffer_t *buf, *base64_buf;

src/login-common/client-common.h

@@ -228,6 +228,8 @@ void client_cmd_starttls(struct client *client);
 
 unsigned int clients_get_count(void) ATTR_PURE;
 
+void client_add_forward_field(struct client *client, const char *key,
+			      const char *value);
 void client_set_title(struct client *client);
 void client_log(struct client *client, const char *msg);
 void client_log_err(struct client *client, const char *msg);