imap-send: gracefully fail if CRAM-MD5 authentication is requested without OpenSSL

Unlike PLAIN, XOAUTH2 and OAUTHBEARER, CRAM-MD5 authentication is not
supported by libcurl and requires OpenSSL. If the user tries to use
CRAM-MD5 authentication without OpenSSL, the previous behaviour was to
attempt to authenticate and fail with a die(error). Handle this in a
better way by first checking if OpenSSL is available and then attempting
to authenticate. If OpenSSL is not available, print an error message and
exit gracefully.

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

Author: AdityaGarg8

imap-send.c

@@ -885,18 +885,6 @@ static char *cram(const char *challenge_64, const char *user, const char *pass)
 	return (char *)response_64;
 }
 
-#else
-
-static char *cram(const char *challenge_64 UNUSED,
-		  const char *user UNUSED,
-		  const char *pass UNUSED)
-{
-	die("If you want to use CRAM-MD5 authenticate method, "
-	    "you have to build git-imap-send with OpenSSL library.");
-}
-
-#endif
-
 static int auth_cram_md5(struct imap_store *ctx, const char *prompt)
 {
 	int ret;
@@ -915,6 +903,12 @@ static int auth_cram_md5(struct imap_store *ctx, const char *prompt)
 	return 0;
 }
 
+#else
+
+#define auth_cram_md5 NULL
+
+#endif
+
 static void server_fill_credential(struct imap_server_conf *srvc, struct credential *cred)
 {
 	if (srvc->user && srvc->pass)
@@ -934,6 +928,38 @@ static void server_fill_credential(struct imap_server_conf *srvc, struct credent
 		srvc->pass = xstrdup(cred->password);
 }
 
+static int try_auth_method(struct imap_server_conf *srvc,
+			   struct imap_store *ctx,
+			   struct imap *imap,
+			   const char *auth_method,
+			   enum CAPABILITY cap,
+			   int (*fn)(struct imap_store *, const char *))
+{
+	struct imap_cmd_cb cb = {0};
+
+	if (!CAP(cap)) {
+		fprintf(stderr, "You specified "
+			"%s as authentication method, "
+			"but %s doesn't support it.\n",
+			auth_method, srvc->host);
+		return -1;
+	}
+	cb.cont = fn;
+
+	if (NOT_CONSTANT(!cb.cont)) {
+		fprintf(stderr, "If you want to use %s authentication mechanism, "
+			"you have to build git-imap-send with OpenSSL library.",
+			auth_method);
+		return -1;
+	}
+	if (imap_exec(ctx, &cb, "AUTHENTICATE %s", auth_method) != RESP_OK) {
+		fprintf(stderr, "IMAP error: AUTHENTICATE %s failed\n",
+			auth_method);
+		return -1;
+	}
+	return 0;
+}
+
 static struct imap_store *imap_open_store(struct imap_server_conf *srvc, const char *folder)
 {
 	struct credential cred = CREDENTIAL_INIT;
@@ -1089,23 +1115,9 @@ static struct imap_store *imap_open_store(struct imap_server_conf *srvc, const c
 		server_fill_credential(srvc, &cred);
 
 		if (srvc->auth_method) {
-			struct imap_cmd_cb cb;
-
 			if (!strcmp(srvc->auth_method, "CRAM-MD5")) {
-				if (!CAP(AUTH_CRAM_MD5)) {
-					fprintf(stderr, "You specified "
-						"CRAM-MD5 as authentication method, "
-						"but %s doesn't support it.\n", srvc->host);
-					goto bail;
-				}
-				/* CRAM-MD5 */
-
-				memset(&cb, 0, sizeof(cb));
-				cb.cont = auth_cram_md5;
-				if (imap_exec(ctx, &cb, "AUTHENTICATE CRAM-MD5") != RESP_OK) {
-					fprintf(stderr, "IMAP error: AUTHENTICATE CRAM-MD5 failed\n");
+				if (try_auth_method(srvc, ctx, imap, "CRAM-MD5", AUTH_CRAM_MD5, auth_cram_md5))
 					goto bail;
-				}
 			} else {
 				fprintf(stderr, "Unknown authentication method:%s\n", srvc->host);
 				goto bail;