thodg/libgit2

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 93b5f20..97c873d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,12 @@ v0.21 + 1
 * The git_transport structure definition has moved into the sys/transport.h
   file.
 
+* The ssh transport supports asking the remote host for accepted
+  credential types as well as multiple challeges using a single
+  connection. This requires to know which username you want to connect
+  as, so this introduces the USERNAME credential type which the ssh
+  transport will use to ask for the username.
+
 * The git_transport_register function no longer takes a priority and takes
   a URL scheme name (eg "http") instead of a prefix like "http://"
 
diff --git a/include/git2/errors.h b/include/git2/errors.h
index c914653..b915606 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -41,6 +41,7 @@ typedef enum {
 	GIT_EMERGECONFLICT  = -13,	/**< Merge conflicts prevented operation */
 	GIT_ELOCKED         = -14,	/**< Lock file prevented operation */
 	GIT_EMODIFIED       = -15,	/**< Reference value does not match expected */
+	GIT_EAUTH           = -16,      /**< Authentication error */
 
 	GIT_PASSTHROUGH     = -30,	/**< Internal only */
 	GIT_ITEROVER        = -31,	/**< Signals end of iteration with iterator */
diff --git a/include/git2/transport.h b/include/git2/transport.h
index 66341d2..7090698 100644
--- a/include/git2/transport.h
+++ b/include/git2/transport.h
@@ -36,6 +36,14 @@ typedef enum {
 
 	/* git_cred_ssh_interactive */
 	GIT_CREDTYPE_SSH_INTERACTIVE = (1u << 4),
+
+	/**
+	 * Username-only information
+	 *
+	 * If the SSH transport does not know which username to use,
+	 * it will ask via this credential type.
+	 */
+	GIT_CREDTYPE_USERNAME = (1u << 5),
 } git_credtype_t;
 
 /* The base structure for all credential types */
@@ -103,6 +111,12 @@ typedef struct git_cred_ssh_custom {
 /** A key for NTLM/Kerberos "default" credentials */
 typedef struct git_cred git_cred_default;
 
+/** Username-only credential information */
+typedef struct git_cred_username {
+	git_cred parent;
+	char username[1];
+} git_cred_username;
+
 /**
  * Check whether a credential object contains username information.
  *
@@ -205,6 +219,14 @@ GIT_EXTERN(int) git_cred_ssh_custom_new(
 GIT_EXTERN(int) git_cred_default_new(git_cred **out);
 
 /**
+ * Create a credential to specify a username.
+ *
+ * This is used with ssh authentication to query for the username if
+ * none is specified in the url.
+ */
+GIT_EXTERN(int) git_cred_username_new(git_cred **cred, const char *username);
+
+/**
  * Signature of a function which acquires a credential object.
  *
  * - cred: The newly created credential object.
diff --git a/script/cibuild.sh b/script/cibuild.sh
index 5ba0746..981f95b 100755
--- a/script/cibuild.sh
+++ b/script/cibuild.sh
@@ -22,7 +22,13 @@ ctest -V . || exit $?
 # can do the push tests over it
 
 killall git-daemon
-sudo start ssh
+
+if [ "$TRAVIS_OS_NAME" = "osx" ]; then
+    echo 'PasswordAuthentication yes' | sudo tee -a /etc/sshd_config
+else
+    sudo start ssh
+fi
+
 ssh-keygen -t rsa -f ~/.ssh/id_rsa -N "" -q
 cat ~/.ssh/id_rsa.pub >>~/.ssh/authorized_keys
 ssh-keyscan -t rsa localhost >>~/.ssh/known_hosts
@@ -34,7 +40,7 @@ export GITTEST_REMOTE_SSH_PUBKEY="$HOME/.ssh/id_rsa.pub"
 export GITTEST_REMOTE_SSH_PASSPHRASE=""
 
 if [ -e ./libgit2_clar ]; then
-    ./libgit2_clar -sonline::push -sonline::clone::cred_callback_failure &&
+    ./libgit2_clar -sonline::push -sonline::clone::cred_callback &&
     rm -rf $HOME/_temp/test.git &&
     git init --bare $HOME/_temp/test.git && # create an empty one
     ./libgit2_clar -sonline::clone::ssh_with_paths
diff --git a/src/transports/cred.c b/src/transports/cred.c
index 913ec36..1b4d29c 100644
--- a/src/transports/cred.c
+++ b/src/transports/cred.c
@@ -17,6 +17,40 @@ int git_cred_has_username(git_cred *cred)
 	return 1;
 }
 
+const char *git_cred__username(git_cred *cred)
+{
+	switch (cred->credtype) {
+	case GIT_CREDTYPE_USERNAME:
+	{
+		git_cred_username *c = (git_cred_username *) cred;
+		return c->username;
+	}
+	case GIT_CREDTYPE_USERPASS_PLAINTEXT:
+	{
+		git_cred_userpass_plaintext *c = (git_cred_userpass_plaintext *) cred;
+		return c->username;
+	}
+	case GIT_CREDTYPE_SSH_KEY:
+	{
+		git_cred_ssh_key *c = (git_cred_ssh_key *) cred;
+		return c->username;
+	}
+	case GIT_CREDTYPE_SSH_CUSTOM:
+	{
+		git_cred_ssh_custom *c = (git_cred_ssh_custom *) cred;
+		return c->username;
+	}
+	case GIT_CREDTYPE_SSH_INTERACTIVE:
+	{
+		git_cred_ssh_interactive *c = (git_cred_ssh_interactive *) cred;
+		return c->username;
+	}
+
+	default:
+		return NULL;
+	}
+}
+
 static void plaintext_free(struct git_cred *cred)
 {
 	git_cred_userpass_plaintext *c = (git_cred_userpass_plaintext *)cred;
@@ -129,6 +163,11 @@ static void default_free(struct git_cred *cred)
 	git__free(c);
 }
 
+static void username_free(struct git_cred *cred)
+{
+	git__free(cred);
+}
+
 int git_cred_ssh_key_new(
 	git_cred **cred,
 	const char *username,
@@ -263,3 +302,22 @@ int git_cred_default_new(git_cred **cred)
 	*cred = c;
 	return 0;
 }
+
+int git_cred_username_new(git_cred **cred, const char *username)
+{
+	git_cred_username *c;
+	size_t len;
+
+	assert(cred);
+
+	len = strlen(username);
+	c = git__malloc(sizeof(git_cred_username) + len + 1);
+	GITERR_CHECK_ALLOC(c);
+
+	c->parent.credtype = GIT_CREDTYPE_USERNAME;
+	c->parent.free = username_free;
+	memcpy(c->username, username, len + 1);
+
+	*cred = (git_cred *) c;
+	return 0;
+}
diff --git a/src/transports/cred.h b/src/transports/cred.h
new file mode 100644
index 0000000..2de8dee
--- /dev/null
+++ b/src/transports/cred.h
@@ -0,0 +1,14 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_git_cred_h__
+#define INCLUDE_git_cred_h__
+
+#include "git2/transport.h"
+
+const char *git_cred__username(git_cred *cred);
+
+#endif
diff --git a/src/transports/cred_helpers.c b/src/transports/cred_helpers.c
index d420e3e..5cc9b08 100644
--- a/src/transports/cred_helpers.c
+++ b/src/transports/cred_helpers.c
@@ -41,6 +41,9 @@ int git_cred_userpass(
 	else
 		return -1;
 
+	if (GIT_CREDTYPE_USERNAME & allowed_types)
+		return git_cred_username_new(cred, effective_username);
+
 	if ((GIT_CREDTYPE_USERPASS_PLAINTEXT & allowed_types) == 0 ||
 			git_cred_userpass_plaintext_new(cred, effective_username, userpass->password) < 0)
 		return -1;
diff --git a/src/transports/ssh.c b/src/transports/ssh.c
index 85f6200..fff8166 100644
--- a/src/transports/ssh.c
+++ b/src/transports/ssh.c
@@ -13,6 +13,7 @@
 #include "buffer.h"
 #include "netops.h"
 #include "smart.h"
+#include "cred.h"
 
 #ifdef GIT_SSH
 
@@ -41,6 +42,8 @@ typedef struct {
 	char *cmd_receivepack;
 } ssh_subtransport;
 
+static int list_auth_methods(int *out, LIBSSH2_SESSION *session, const char *username);
+
 static void ssh_error(LIBSSH2_SESSION *session, const char *errmsg)
 {
 	char *ssherr;
@@ -354,6 +357,9 @@ static int _git_ssh_authenticate_session(
 		}
 	} while (LIBSSH2_ERROR_EAGAIN == rc || LIBSSH2_ERROR_TIMEOUT == rc);
 
+        if (rc == LIBSSH2_ERROR_PASSWORD_EXPIRED || rc == LIBSSH2_ERROR_AUTHENTICATION_FAILED)
+                return GIT_EAUTH;
+
 	if (rc != LIBSSH2_ERROR_NONE) {
 		ssh_error(session, "Failed to authenticate SSH session");
 		return -1;
@@ -362,6 +368,43 @@ static int _git_ssh_authenticate_session(
 	return 0;
 }
 
+static int request_creds(git_cred **out, ssh_subtransport *t, const char *user, int auth_methods)
+{
+	int error, no_callback = 0;
+	git_cred *cred = NULL;
+
+	if (!t->owner->cred_acquire_cb) {
+		no_callback = 1;
+	} else {
+		error = t->owner->cred_acquire_cb(&cred, t->owner->url, user, auth_methods,
+						  t->owner->cred_acquire_payload);
+
+		if (error == GIT_PASSTHROUGH)
+			no_callback = 1;
+		else if (error < 0)
+			return error;
+		else if (!cred) {
+			giterr_set(GITERR_SSH, "Callback failed to initialize SSH credentials");
+			return -1;
+		}
+	}
+
+	if (no_callback) {
+		giterr_set(GITERR_SSH, "authentication required but no callback set");
+		return -1;
+	}
+
+	if (!(cred->credtype & auth_methods)) {
+		cred->free(cred);
+		giterr_set(GITERR_SSH, "callback returned unsupported credentials type");
+		return -1;
+	}
+
+	*out = cred;
+
+	return 0;
+}
+
 static int _git_ssh_session_create(
 	LIBSSH2_SESSION** session,
 	gitno_socket socket)
@@ -402,8 +445,9 @@ static int _git_ssh_setup_conn(
 {
 	char *host=NULL, *port=NULL, *path=NULL, *user=NULL, *pass=NULL;
 	const char *default_port="22";
-	int no_callback = 0;
+	int auth_methods, error = 0;
 	ssh_stream *s;
+	git_cred *cred = NULL;
 	LIBSSH2_SESSION* session=NULL;
 	LIBSSH2_CHANNEL* channel=NULL;
 
@@ -414,56 +458,68 @@ static int _git_ssh_setup_conn(
 	s = (ssh_stream *)*stream;
 
 	if (!git__prefixcmp(url, prefix_ssh)) {
-		if (gitno_extract_url_parts(&host, &port, &path, &user, &pass, url, default_port) < 0)
+		if ((error = gitno_extract_url_parts(&host, &port, &path, &user, &pass, url, default_port)) < 0)
 			goto on_error;
 	} else {
-		if (git_ssh_extract_url_parts(&host, &user, url) < 0)
+		if ((error = git_ssh_extract_url_parts(&host, &user, url)) < 0)
 			goto on_error;
 		port = git__strdup(default_port);
 		GITERR_CHECK_ALLOC(port);
 	}
 
-	if (gitno_connect(&s->socket, host, port, 0) < 0)
-		goto on_error;
-
-	if (user && pass) {
-		if (git_cred_userpass_plaintext_new(&t->cred, user, pass) < 0)
+	/* we need the username to ask for auth methods */
+	if (!user) {
+		if ((error = request_creds(&cred, t, NULL, GIT_CREDTYPE_USERNAME)) < 0)
 			goto on_error;
-	} else if (!t->owner->cred_acquire_cb) {
-		no_callback = 1;
-	} else {
-		int error;
-		error = t->owner->cred_acquire_cb(&t->cred, t->owner->url, user,
-			GIT_CREDTYPE_USERPASS_PLAINTEXT |
-			GIT_CREDTYPE_SSH_KEY | GIT_CREDTYPE_SSH_CUSTOM |
-			GIT_CREDTYPE_SSH_INTERACTIVE,
-			t->owner->cred_acquire_payload);
 
-		if (error == GIT_PASSTHROUGH)
-			no_callback = 1;
-		else if (error < 0)
+		user = git__strdup(((git_cred_username *) cred)->username);
+		cred->free(cred);
+		cred = NULL;
+		if (!user)
 			goto on_error;
-		else if (!t->cred) {
-			giterr_set(GITERR_SSH, "Callback failed to initialize SSH credentials");
+	} else if (user && pass) {
+		if ((error = git_cred_userpass_plaintext_new(&cred, user, pass)) < 0)
 			goto on_error;
-		}
 	}
 
-	if (no_callback) {
-		giterr_set(GITERR_SSH, "authentication required but no callback set");
+	if ((error = gitno_connect(&s->socket, host, port, 0)) < 0)
 		goto on_error;
-	}
 
-	assert(t->cred);
+	if ((error = _git_ssh_session_create(&session, s->socket)) < 0)
+		goto on_error;
 
-	if (_git_ssh_session_create(&session, s->socket) < 0)
+	if ((error = list_auth_methods(&auth_methods, session, user)) < 0)
 		goto on_error;
 
-	if (_git_ssh_authenticate_session(session, t->cred) < 0)
+	error = GIT_EAUTH;
+	/* if we already have something to try */
+	if (cred && auth_methods & cred->credtype)
+		error = _git_ssh_authenticate_session(session, cred);
+
+	while (error == GIT_EAUTH) {
+		if (cred) {
+			cred->free(cred);
+			cred = NULL;
+		}
+
+		if ((error = request_creds(&cred, t, user, auth_methods)) < 0)
+			goto on_error;
+
+		if (strcmp(user, git_cred__username(cred))) {
+			giterr_set(GITERR_SSH, "username does not match previous request");
+			error = -1;
+			goto on_error;
+		}
+
+		error = _git_ssh_authenticate_session(session, cred);
+	}
+
+	if (error < 0)
 		goto on_error;
 
 	channel = libssh2_channel_open_session(session);
 	if (!channel) {
+		error = -1;
 		ssh_error(session, "Failed to open SSH channel");
 		goto on_error;
 	}
@@ -474,6 +530,9 @@ static int _git_ssh_setup_conn(
 	s->channel = channel;
 
 	t->current_stream = s;
+	if (cred)
+		cred->free(cred);
+
 	git__free(host);
 	git__free(port);
 	git__free(path);
@@ -490,6 +549,9 @@ on_error:
 	if (*stream)
 		ssh_stream_free(*stream);
 
+	if (cred)
+		cred->free(cred);
+
 	git__free(host);
 	git__free(port);
 	git__free(user);
@@ -498,7 +560,7 @@ on_error:
 	if (session)
 		libssh2_session_free(session);
 
-	return -1;
+	return error;
 }
 
 static int ssh_uploadpack_ls(
@@ -508,10 +570,7 @@ static int ssh_uploadpack_ls(
 {
 	const char *cmd = t->cmd_uploadpack ? t->cmd_uploadpack : cmd_uploadpack;
 
-	if (_git_ssh_setup_conn(t, url, cmd, stream) < 0)
-		return -1;
-
-	return 0;
+	return _git_ssh_setup_conn(t, url, cmd, stream);
 }
 
 static int ssh_uploadpack(
@@ -606,6 +665,53 @@ static void _ssh_free(git_smart_subtransport *subtransport)
 	git__free(t->cmd_receivepack);
 	git__free(t);
 }
+
+#define SSH_AUTH_PUBLICKEY "publickey"
+#define SSH_AUTH_PASSWORD "password"
+#define SSH_AUTH_KEYBOARD_INTERACTIVE "keyboard-interactive"
+
+static int list_auth_methods(int *out, LIBSSH2_SESSION *session, const char *username)
+{
+	const char *list, *ptr;
+
+	*out = 0;
+
+	list = libssh2_userauth_list(session, username, strlen(username));
+
+	/* either error, or the remote accepts NONE auth, which is bizarre, let's punt */
+	if (list == NULL && !libssh2_userauth_authenticated(session))
+		return -1;
+
+	ptr = list;
+	while (ptr) {
+		if (*ptr == ',')
+			ptr++;
+
+		if (!git__prefixcmp(ptr, SSH_AUTH_PUBLICKEY)) {
+			*out |= GIT_CREDTYPE_SSH_KEY;
+			*out |= GIT_CREDTYPE_SSH_CUSTOM;
+			ptr += strlen(SSH_AUTH_PUBLICKEY);
+			continue;
+		}
+
+		if (!git__prefixcmp(ptr, SSH_AUTH_PASSWORD)) {
+			*out |= GIT_CREDTYPE_USERPASS_PLAINTEXT;
+			ptr += strlen(SSH_AUTH_PASSWORD);
+			continue;
+		}
+
+		if (!git__prefixcmp(ptr, SSH_AUTH_KEYBOARD_INTERACTIVE)) {
+			*out |= GIT_CREDTYPE_SSH_INTERACTIVE;
+			ptr += strlen(SSH_AUTH_KEYBOARD_INTERACTIVE);
+			continue;
+		}
+
+		/* Skipt it if we don't know it */
+		ptr = strchr(ptr, ',');
+	}
+
+	return 0;
+}
 #endif
 
 int git_smart_subtransport_ssh(
diff --git a/tests/online/clone.c b/tests/online/clone.c
index 0cd0f31..c935965 100644
--- a/tests/online/clone.c
+++ b/tests/online/clone.c
@@ -12,6 +12,8 @@
 #define BB_REPO_URL_WITH_PASS "https://libgit3:libgit3@bitbucket.org/libgit2/testgitrepository.git"
 #define BB_REPO_URL_WITH_WRONG_PASS "https://libgit3:wrong@bitbucket.org/libgit2/testgitrepository.git"
 
+#define SSH_REPO_URL "ssh://github.com/libgit2/TestGitRepository"
+
 static git_repository *g_repo;
 static git_clone_options g_options;
 
@@ -222,8 +224,41 @@ void test_online_clone__cred_callback_failure_return_code_is_tunnelled(void)
 
 	g_options.remote_callbacks.credentials = cred_failure_cb;
 
-	/* TODO: this should expect -172. */
-	cl_git_fail_with(git_clone(&g_repo, remote_url, "./foo", &g_options), -1);
+	cl_git_fail_with(-172, git_clone(&g_repo, remote_url, "./foo", &g_options));
+}
+
+static int cred_count_calls_cb(git_cred **cred, const char *url, const char *user,
+			       unsigned int allowed_types, void *data)
+{
+	size_t *counter = (size_t *) data;
+
+	GIT_UNUSED(url); GIT_UNUSED(user); GIT_UNUSED(allowed_types);
+
+	if (allowed_types == GIT_CREDTYPE_USERNAME)
+		return git_cred_username_new(cred, "foo");
+
+	(*counter)++;
+
+	if (*counter == 3)
+		return GIT_EUSER;
+
+	return git_cred_userpass_plaintext_new(cred, "foo", "bar");
+}
+
+void test_online_clone__cred_callback_called_again_on_auth_failure(void)
+{
+	const char *remote_url = cl_getenv("GITTEST_REMOTE_URL");
+	const char *remote_user = cl_getenv("GITTEST_REMOTE_USER");
+	size_t counter = 0;
+
+	if (!remote_url || !remote_user)
+		clar__skip();
+
+	g_options.remote_callbacks.credentials = cred_count_calls_cb;
+	g_options.remote_callbacks.payload = &counter;
+
+	cl_git_fail_with(GIT_EUSER, git_clone(&g_repo, remote_url, "./foo", &g_options));
+	cl_assert_equal_i(3, counter);
 }
 
 int cred_default(
@@ -328,6 +363,36 @@ static int cred_cb(git_cred **cred, const char *url, const char *user_from_url,
 	return -1;
 }
 
+static int check_ssh_auth_methods(git_cred **cred, const char *url, const char *username_from_url,
+				  unsigned int allowed_types, void *data)
+{
+	int *with_user = (int *) data;
+	GIT_UNUSED(cred); GIT_UNUSED(url); GIT_UNUSED(username_from_url); GIT_UNUSED(data);
+
+	if (!*with_user)
+		cl_assert_equal_i(GIT_CREDTYPE_USERNAME, allowed_types);
+	else
+		cl_assert(!(allowed_types & GIT_CREDTYPE_USERNAME));
+
+	return GIT_EUSER;
+}
+
+void test_online_clone__ssh_auth_methods(void)
+{
+	int with_user;
+
+	g_options.remote_callbacks.credentials = check_ssh_auth_methods;
+	g_options.remote_callbacks.payload = &with_user;
+
+	with_user = 0;
+	cl_git_fail_with(GIT_EUSER,
+		git_clone(&g_repo, SSH_REPO_URL, "./foo", &g_options));
+
+	with_user = 1;
+	cl_git_fail_with(GIT_EUSER,
+		git_clone(&g_repo, "ssh://git@github.com/libgit2/TestGitRepository", "./foo", &g_options));
+}
+
 static int custom_remote_ssh_with_paths(
 	git_remote **out,
 	git_repository *repo,
@@ -336,7 +401,6 @@ static int custom_remote_ssh_with_paths(
 	void *payload)
 {
 	int error;
-
 	git_remote_callbacks callbacks = GIT_REMOTE_CALLBACKS_INIT;
 
 	if ((error = git_remote_create(out, repo, name, url)) < 0)
@@ -381,3 +445,18 @@ void test_online_clone__ssh_with_paths(void)
 	cl_git_pass(git_clone(&g_repo, remote_url, "./foo", &g_options));
 }
 
+static int cred_foo_bar(git_cred **cred, const char *url, const char *username_from_url,
+				  unsigned int allowed_types, void *data)
+
+{
+	GIT_UNUSED(url); GIT_UNUSED(username_from_url); GIT_UNUSED(allowed_types); GIT_UNUSED(data);
+
+	return git_cred_userpass_plaintext_new(cred, "foo", "bar");
+}
+
+void test_online_clone__ssh_cannot_change_username(void)
+{
+	g_options.remote_callbacks.credentials = cred_foo_bar;
+
+	cl_git_fail(git_clone(&g_repo, "ssh://git@github.com/libgit2/TestGitRepository", "./foo", &g_options));
+}
diff --git a/tests/online/push.c b/tests/online/push.c
index c351827..4d88bdf 100644
--- a/tests/online/push.c
+++ b/tests/online/push.c
@@ -50,6 +50,15 @@ static int cred_acquire_cb(
 	GIT_UNUSED(user_from_url);
 	GIT_UNUSED(payload);
 
+	if (GIT_CREDTYPE_USERNAME & allowed_types) {
+		if (!_remote_user) {
+			printf("GITTEST_REMOTE_USER must be set\n");
+			return -1;
+		}
+
+		return git_cred_username_new(cred, _remote_user);
+	}
+
 	if (GIT_CREDTYPE_DEFAULT & allowed_types) {
 		if (!_remote_default) {
 			printf("GITTEST_REMOTE_DEFAULT must be set to use NTLM/Negotiate credentials\n");