4 files changed, 23 insertions, 5 deletions
diff --git a/src/transports/http.c b/src/transports/http.c
index 51219963c..7f9d35012 100644
--- a/src/transports/http.c
+++ b/src/transports/http.c
@@ -371,6 +371,7 @@ static int on_headers_complete(http_parser *parser)
 								  allowed_auth_types,
 								  t->owner->cred_acquire_payload);
 
+				/* treat GIT_PASSTHROUGH as if callback isn't set */
 				if (error == GIT_PASSTHROUGH) {
 					no_callback = 1;
 				} else if (error < 0) {
@@ -639,6 +640,9 @@ static int http_connect(http_subtransport *t)
 		giterr_clear();
 		error = t->owner->certificate_check_cb(cert, is_valid, t->connection_data.host, t->owner->message_cb_payload);
 
+		if (error == GIT_PASSTHROUGH)
+			error = is_valid ? 0 : GIT_ECERTIFICATE;
+
 		if (error < 0) {
 			if (!giterr_last())
 				giterr_set(GITERR_NET, "user cancelled certificate check");
diff --git a/src/transports/smart.c b/src/transports/smart.c
index e972d30ba..9fcbdcf21 100644
--- a/src/transports/smart.c
+++ b/src/transports/smart.c
@@ -481,6 +481,11 @@ int git_transport_smart_certificate_check(git_transport *transport, git_cert *ce
 {
 	transport_smart *t = (transport_smart *)transport;
 
+	assert(transport && cert && hostname);
+
+	if (!t->certificate_check_cb)
+		return GIT_PASSTHROUGH;
+
 	return t->certificate_check_cb(cert, valid, hostname, t->message_cb_payload);
 }
 
@@ -488,6 +493,11 @@ int git_transport_smart_credentials(git_cred **out, git_transport *transport, co
 {
 	transport_smart *t = (transport_smart *)transport;
 
+	assert(out && transport);
+
+	if (!t->cred_acquire_cb)
+		return GIT_PASSTHROUGH;
+
 	return t->cred_acquire_cb(out, t->url, user, methods, t->cred_acquire_payload);
 }
 
diff --git a/src/transports/ssh.c b/src/transports/ssh.c
index 7d9114c26..9e01a4aea 100644
--- a/src/transports/ssh.c
+++ b/src/transports/ssh.c
@@ -447,11 +447,11 @@ static int request_creds(git_cred **out, ssh_subtransport *t, const char *user,
 		error = t->owner->cred_acquire_cb(&cred, t->owner->url, user, auth_methods,
 						  t->owner->cred_acquire_payload);
 
-		if (error == GIT_PASSTHROUGH)
+		if (error == GIT_PASSTHROUGH) {
 			no_callback = 1;
-		else if (error < 0)
+		} else if (error < 0) {
 			return error;
-		else if (!cred) {
+		} else if (!cred) {
 			giterr_set(GITERR_SSH, "callback failed to initialize SSH credentials");
 			return -1;
 		}
@@ -584,7 +584,8 @@ post_extract:
 		cert_ptr = &cert;
 
 		error = t->owner->certificate_check_cb((git_cert *) cert_ptr, 0, host, t->owner->message_cb_payload);
-		if (error < 0) {
+
+		if (error < 0 && error != GIT_PASSTHROUGH) {
 			if (!giterr_last())
 				giterr_set(GITERR_NET, "user cancelled hostkey check");
 
diff --git a/src/transports/winhttp.c b/src/transports/winhttp.c
index e925dbdc0..5e7bde73c 100644
--- a/src/transports/winhttp.c
+++ b/src/transports/winhttp.c
@@ -228,7 +228,7 @@ static int fallback_cred_acquire_cb(
 		}
 
 		hCoInitResult = CoInitializeEx(NULL, COINIT_MULTITHREADED);
-			
+
 		if (SUCCEEDED(hCoInitResult) || hCoInitResult == RPC_E_CHANGED_MODE) {
 			IInternetSecurityManager* pISM;
 
@@ -295,6 +295,9 @@ static int certificate_check(winhttp_stream *s, int valid)
 	error = t->owner->certificate_check_cb((git_cert *) &cert, valid, t->connection_data.host, t->owner->message_cb_payload);
 	CertFreeCertificateContext(cert_ctx);
 
+	if (error == GIT_PASSTHROUGH)
+		error = valid ? 0 : GIT_ECERTIFICATE;
+
 	if (error < 0 && !giterr_last())
 		giterr_set(GITERR_NET, "user cancelled certificate check");