maintenance: configure credentials to be silent

When background maintenance attempts to perform a prefetch to remote servers, this may trigger authentication requirements. If the credentials are expired, then the credential helper may need user input in order to get refreshed credentials. It is not a good experience for users to get credential pop-ups when not directly interacting with Git.

Add a new configuration value, 'credential.interactive', to specify to the credential helper that it should not prompt for user interaction. This option has been respected by Git Credential Manager since 2020 [1], so this is now presenting it as an official Git config value.

These changes were first merged into the microsoft/git fork in August 2023
[2] but were not upstreamed immediately. The change has been a positive one for users of that fork, as they no longer get pop-ups and they also are not getting maintenance.lock file blocks when the prefetch task waits for credentials. This has become even more important recently as credential lifetimes have been restricted significantly, leading to a higher likelihood that this will happen during a background prefetch.

I was reminded of these changes when liuzhongbo started a discussion [3] about maintenance.lock files and requesting that they are removed if they are stale. This does not address that issue directly, but is an important way to reduce the lifetime of maintenance.lock files when blocked on credential prompts.

[1] https://github.com/git-ecosystem/git-credential-manager/pull/91

[2] https://github.com/microsoft/git/pull/598

[3]
https://lore.kernel.org/git/[email protected]/T/#t

Thanks, -Stolee

Derrick Stolee (3):
credential: add new interactive config option
maintenance: add custom config to background jobs
scalar: configure maintenance during 'reconfigure'

 Documentation/config/credential.txt |  8 +++++
 builtin/gc.c                        | 53 +++++++++++++++++++++++++----
 credential.c                        | 30 ++++++++++++++--
 scalar.c                            |  3 ++
 t/t5551-http-fetch-smart.sh         | 22 ++++++++++++
 t/t7900-maintenance.sh              |  3 ++
 t/t9210-scalar.sh                   |  7 ++--
 7 files changed, 114 insertions(+), 12 deletions(-)

base-commit: 6531f31ef3bead57a3255fa08efa6e7553c5a9a7
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1798%2Fderrickstolee%2Fbackground-quiet-credentials-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1798/derrickstolee/background-quiet-credentials-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1798

gitgitgadget

From: Derrick Stolee <[email protected]>

When scripts or background maintenance wish to perform HTTP(S) requests, there is a risk that our stored credentials might be invalid. At the moment, this causes the credential helper to ping the user and block the process. Even if the credential helper does not ping the user, Git falls back to the 'askpass' method, which includes a direct ping to the user via the terminal.

Even setting the 'core.askPass' config as something like 'echo' will causes Git to fallback to a terminal prompt. It uses git_terminal_prompt(), which finds the terminal from the environment and ignores whether stdin has been redirected. This can also block the process awaiting input.

Create a new config option to prevent user interaction, favoring a failure to a blocked process.

The chosen name, 'credential.interactive', is taken from the config option used by Git Credential Manager to already avoid user interactivity, so there is already one credential helper that integrates with this option. However, older versions of Git Credential Manager also accepted other string values, including 'auto', 'never', and 'always'. The modern use is to use a boolean value, but we should still be careful that some users could have these non-booleans. Further, we should respect 'never' the same as 'false'. This is respected by the implementation and test, but not mentioned in the documentation.

The implementation for the Git interactions takes place within credential_getpass(). The method prototype is modified to return an 'int' instead of 'void'. This allows us to detect that no attempt was made to fill the given credential, changing the single caller slightly.

Also, a new trace2 region is added around the interactive portion of the credential request. This provides a way to measure the amount of time spent in that region for commands that _are_ interactive. It also makes a conventient way to test that the config option works with 'test_region'.

---
 Documentation/config/credential.txt |  8 ++++++++
 credential.c                        | 30 ++++++++++++++++++++++++++---
 t/t5551-http-fetch-smart.sh         | 22 +++++++++++++++++++++
 3 files changed, 57 insertions(+), 3 deletions(-)

index 0221c3e620d..470482ff4c2 100644
@@ -9,6 +9,14 @@ credential.helper::
 Note that multiple helpers may be defined. See linkgit:gitcredentials[7]
 for details and examples.
 
+credential.interactive::
+	By default, Git and any configured credential helpers will ask for
+	user input when new credentials are required. Many of these helpers
+	will succeed based on stored credentials if those credentials are
+	still valid. To avoid the possibility of user interactivity from
+	Git, set `credential.interactive=false`. Some credential helpers
+	respect this option as well.
+
 credential.useHttpPath::
 	When acquiring credentials, consider the "path" component of an http
 	or https URL to be important. Defaults to false. See

index ee46351ce01..6dea3859ece 100644
@@ -13,6 +13,8 @@
 #include "strbuf.h"
 #include "urlmatch.h"
 #include "git-compat-util.h"
+#include "trace2.h"
+#include "repository.h"
 
 void credential_init(struct credential *c)
 {

@@ -251,14 +253,36 @@ static char *credential_ask_one(const char *what, struct credential *c,
 	return xstrdup(r);
 }
 
-static void credential_getpass(struct credential *c)
+static int credential_getpass(struct credential *c)
 {
+	int interactive;
+	char *value;
+	if (!git_config_get_maybe_bool("credential.interactive", &interactive) &&
+	    !interactive) {
+		trace2_data_intmax("credential", the_repository,
+				   "interactive/skipped", 1);
+		return -1;
+	}
+	if (!git_config_get_string("credential.interactive", &value)) {
+		int same = !strcmp(value, "never");
+		free(value);
+		if (same) {
+			trace2_data_intmax("credential", the_repository,
+					   "interactive/skipped", 1);
+			return -1;
+		}
+	}
+
+	trace2_region_enter("credential", "interactive", the_repository);
 	if (!c->username)
 		c->username = credential_ask_one("Username", c,
 						 PROMPT_ASKPASS|PROMPT_ECHO);
 	if (!c->password)
 		c->password = credential_ask_one("Password", c,
 						 PROMPT_ASKPASS);
+	trace2_region_leave("credential", "interactive", the_repository);
+
+	return 0;
 }
 
 int credential_has_capability(const struct credential_capability *capa,

@@ -501,8 +525,8 @@ void credential_fill(struct credential *c, int all_capabilities)
 			    c->helpers.items[i].string);
 	}
 
-	credential_getpass(c);
-	if (!c->username && !c->password && !c->credential)
+	if (credential_getpass(c) ||
+	    (!c->username && !c->password && !c->credential))
 		die("unable to get password from user");
 }
 

index 7b5ab0eae16..ceb3336a5c4 100755
@@ -186,6 +186,28 @@ test_expect_success 'clone from password-protected repository' '
 	test_cmp expect actual
 '
 
+test_expect_success 'credential.interactive=false skips askpass' '
+	set_askpass bogus nonsense &&
+	(
+		GIT_TRACE2_EVENT="$(pwd)/interactive-true" &&
+		export GIT_TRACE2_EVENT &&
+		test_must_fail git clone --bare "$HTTPD_URL/auth/smart/repo.git" interactive-true-dir &&
+		test_region credential interactive interactive-true &&
+
+		GIT_TRACE2_EVENT="$(pwd)/interactive-false" &&
+		export GIT_TRACE2_EVENT &&
+		test_must_fail git -c credential.interactive=false \
+			clone --bare "$HTTPD_URL/auth/smart/repo.git" interactive-false-dir &&
+		test_region ! credential interactive interactive-false &&
+
+		GIT_TRACE2_EVENT="$(pwd)/interactive-never" &&
+		export GIT_TRACE2_EVENT &&
+		test_must_fail git -c credential.interactive=never \
+			clone --bare "$HTTPD_URL/auth/smart/repo.git" interactive-never-dir &&
+		test_region ! credential interactive interactive-never
+	)
+'
+
 test_expect_success 'clone from auth-only-for-push repository' '
 	echo two >expect &&
 	set_askpass wrong &&

gitgitgadget

From: Derrick Stolee <[email protected]>

At the moment, some background jobs are getting blocked on credentials during the 'prefetch' task. This leads to other tasks, such as incremental repacks, getting blocked. Further, if a user manages to fix their credentials, then they still need to cancel the background process before their background maintenance can continue working.

Update the background schedules for our four scheduler integrations to include these config options via '-c' options:

* 'credential.interactive=false' will stop Git and some credential helpers from prompting in the UI (assuming the '-c' parameters are carried through and respected by GCM).

* 'core.askPass=true' will replace the text fallback for a username and password into the 'true' command, which will return a success in its exit code, but Git will treat the empty string returned as an invalid password and move on.

We can do some testing that the credentials are passed, at least in the systemd case due to writing the service files.

---
 builtin/gc.c           | 53 ++++++++++++++++++++++++++++++++++++------
 t/t7900-maintenance.sh |  3 +++
 2 files changed, 49 insertions(+), 7 deletions(-)

index 7dac9714054..fb1be542e06 100644
@@ -1766,6 +1766,42 @@ static const char *get_frequency(enum schedule_priority schedule)
 	}
 }
 
+static const char *extraconfig[] = {
+	"credential.interactive=false",
+	"core.askPass=true", /* 'true' returns success, but no output. */
+	NULL
+};
+
+static const char *get_extra_config_parameters(void) {
+	static const char *result = NULL;
+	struct strbuf builder = STRBUF_INIT;
+
+	if (result)
+		return result;
+
+	for (const char **s = extraconfig; s && *s; s++)
+		strbuf_addf(&builder, "-c %s ", *s);
+
+	result = strbuf_detach(&builder, NULL);
+	return result;
+}
+
+static const char *get_extra_launchctl_strings(void) {
+	static const char *result = NULL;
+	struct strbuf builder = STRBUF_INIT;
+
+	if (result)
+		return result;
+
+	for (const char **s = extraconfig; s && *s; s++) {
+		strbuf_addstr(&builder, "<string>-c</string>\n");
+		strbuf_addf(&builder, "<string>%s</string>\n", *s);
+	}
+
+	result = strbuf_detach(&builder, NULL);
+	return result;
+}
+
 /*
  * get_schedule_cmd` reads the GIT_TEST_MAINT_SCHEDULER environment variable
  * to mock the schedulers that `git maintenance start` rely on.

@@ -1972,6 +2008,7 @@ static int launchctl_schedule_plist(const char *exec_path, enum schedule_priorit
 		   "<array>\n"
 		   "<string>%s/git</string>\n"
 		   "<string>--exec-path=%s</string>\n"
+		   "%s" /* For extra config parameters. */
 		   "<string>for-each-repo</string>\n"
 		   "<string>--keep-going</string>\n"
 		   "<string>--config=maintenance.repo</string>\n"

@@ -1981,7 +2018,8 @@ static int launchctl_schedule_plist(const char *exec_path, enum schedule_priorit
 		   "</array>\n"
 		   "<key>StartCalendarInterval</key>\n"
 		   "<array>\n";
-	strbuf_addf(&plist, preamble, name, exec_path, exec_path, frequency);
+	strbuf_addf(&plist, preamble, name, exec_path, exec_path,
+		    get_extra_launchctl_strings(), frequency);
 
 	switch (schedule) {
 	case SCHEDULE_HOURLY:

@@ -2216,11 +2254,12 @@ static int schtasks_schedule_task(const char *exec_path, enum schedule_priority
 	      "<Actions Context=\"Author\">\n"
 	      "<Exec>\n"
 	      "<Command>\"%s\\headless-git.exe\"</Command>\n"
-	      "<Arguments>--exec-path=\"%s\" for-each-repo --keep-going --config=maintenance.repo maintenance run --schedule=%s</Arguments>\n"
+	      "<Arguments>--exec-path=\"%s\" %s for-each-repo --keep-going --config=maintenance.repo maintenance run --schedule=%s</Arguments>\n"
 	      "</Exec>\n"
 	      "</Actions>\n"
 	      "</Task>\n";
-	fprintf(tfile->fp, xml, exec_path, exec_path, frequency);
+	fprintf(tfile->fp, xml, exec_path, exec_path,
+		get_extra_config_parameters(), frequency);
 	strvec_split(&child.args, cmd);
 	strvec_pushl(&child.args, "/create", "/tn", name, "/f", "/xml",
 				  get_tempfile_path(tfile), NULL);

@@ -2361,8 +2400,8 @@ static int crontab_update_schedule(int run_maintenance, int fd)
 			"# replaced in the future by a Git command.\n\n");
 
 		strbuf_addf(&line_format,
-			    "%%d %%s * * %%s \"%s/git\" --exec-path=\"%s\" for-each-repo --keep-going --config=maintenance.repo maintenance run --schedule=%%s\n",
-			    exec_path, exec_path);
+			    "%%d %%s * * %%s \"%s/git\" --exec-path=\"%s\" %s for-each-repo --keep-going --config=maintenance.repo maintenance run --schedule=%%s\n",
+			    exec_path, exec_path, get_extra_config_parameters());
 		fprintf(cron_in, line_format.buf, minute, "1-23", "*", "hourly");
 		fprintf(cron_in, line_format.buf, minute, "0", "1-6", "daily");
 		fprintf(cron_in, line_format.buf, minute, "0", "0", "weekly");

@@ -2562,7 +2601,7 @@ static int systemd_timer_write_service_template(const char *exec_path)
 	       "\n"
 	       "[Service]\n"
 	       "Type=oneshot\n"
-	       "ExecStart=\"%s/git\" --exec-path=\"%s\" for-each-repo --keep-going --config=maintenance.repo maintenance run --schedule=%%i\n"
+	       "ExecStart=\"%s/git\" --exec-path=\"%s\" %s for-each-repo --keep-going --config=maintenance.repo maintenance run --schedule=%%i\n"
 	       "LockPersonality=yes\n"
 	       "MemoryDenyWriteExecute=yes\n"
 	       "NoNewPrivileges=yes\n"

@@ -2572,7 +2611,7 @@ static int systemd_timer_write_service_template(const char *exec_path)
 	       "RestrictSUIDSGID=yes\n"
 	       "SystemCallArchitectures=native\n"
 	       "SystemCallFilter=@system-service\n";
-	if (fprintf(file, unit, exec_path, exec_path) < 0) {
+	if (fprintf(file, unit, exec_path, exec_path, get_extra_config_parameters()) < 0) {
 		error(_("failed to write to '%s'"), filename);
 		fclose(file);
 		goto error;

index abae7a97546..3cd7e1fcacb 100755
@@ -825,6 +825,9 @@ test_expect_success 'start and stop Linux/systemd maintenance' '
 	test_systemd_analyze_verify "systemd/user/[email protected]" &&
 	test_systemd_analyze_verify "systemd/user/[email protected]" &&
 
+	grep "core.askPass=true" "systemd/user/[email protected]" &&
+	grep "credential.interactive=false" "systemd/user/[email protected]" &&
+
 	printf -- "--user enable --now git-maintenance@%s.timer\n" hourly daily weekly >expect &&
 	test_cmp expect args &&
 

gitgitgadget

From: Derrick Stolee <[email protected]>

The 'scalar reconfigure' command is intended to update registered repos with the latest settings available. However, up to now we were not reregistering the repos with background maintenance.

In particular, this meant that the background maintenance schedule would not be updated if there are improvements between versions.

Be sure to register repos for maintenance during the reconfigure step.

---
 scalar.c          | 3 +++
 t/t9210-scalar.sh | 7 +++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

index 09560aeab54..73b79a5d4c9 100644
@@ -733,6 +733,9 @@ static int cmd_reconfigure(int argc, const char **argv)
 
 		the_repository = old_repo;
 
+		if (toggle_maintenance(1) >= 0)
+			succeeded = 1;
+
 loop_end:
 		if (!succeeded) {
 			res = -1;

index e8613990e13..027235d61aa 100755
@@ -194,8 +194,11 @@ test_expect_success 'scalar reconfigure' '
 	scalar reconfigure one &&
 	test true = "$(git -C one/src config core.preloadIndex)" &&
 	git -C one/src config core.preloadIndex false &&
-	scalar reconfigure -a &&
-	test true = "$(git -C one/src config core.preloadIndex)"
+	rm one/src/cron.txt &&
+	GIT_TRACE2_EVENT="$(pwd)/reconfigure" scalar reconfigure -a &&
+	test_path_is_file one/src/cron.txt &&
+	test true = "$(git -C one/src config core.preloadIndex)" &&
+	test_subcommand git maintenance start <reconfigure
 '
 
 test_expect_success 'scalar reconfigure --all with includeIf.onbranch' '

gitgitgadget

So, the other helpers are also supposed to check for the variable and fail when it has to go interactive now.

Sounds good.

I would hold off from saying "supposed to" but Git is definitely hinting towards that behavior.

Perhaps I'm just hung up on the idea that we are not adding a new wrinkle to the "contract" but recommending a good thing that was previously not part of the interaction.

Thanks,
-Stolee

I would too. I didn't mean "they were behaving correctly, but we changed the rules from under them and they need to be fixed". With or without your patch, they would try to go interactive and make the process get stuck, until they start to check if they should refrain from going interactive. With your patch, they have a way to do that check in a documented way.