Add "--password-file-reload" flag to refresh password during each sync cycle (#976)

* add-password-file-reload-flag

* Update main.go

Co-authored-by: Tim Hockin <thockin@google.com>

* Remove password file reload functionality

Removed the password file reload flag and related logic to simplify credential management.

* Simplify comment about token rotation

Removed redundant mention of 'from Vault' in comment.

* Implement password-file reload test in e2e script

Add end-to-end test for password-file reload during sync.

* Fix indentation in comments for clarity

* Format

* Update main.go

Co-authored-by: Tim Hockin <thockin@google.com>

* rename e2e test function & add max-attempts flag

---------

Co-authored-by: Tim Hockin <thockin@google.com>

Author: vaibhavdesai137

main.go

@@ -749,19 +749,6 @@ func main() {
 		os.Exit(1)
 	}
 
-	// Finish populating credentials.
-	for i := range *flCredentials {
-		cred := &(*flCredentials)[i]
-		if cred.PasswordFile != "" {
-			passwordFileBytes, err := os.ReadFile(cred.PasswordFile)
-			if err != nil {
-				log.Error(err, "can't read password file", "file", cred.PasswordFile)
-				os.Exit(1)
-			}
-			cred.Password = string(passwordFileBytes)
-		}
-	}
-
 	// If the --repo or any submodule uses SSH, we need to know which keys.
 	if err := git.SetupGitSSH(*flSSHKnownHosts, *flSSHKeyFiles, *flSSHKnownHostsFile); err != nil {
 		log.Error(err, "can't set up git SSH", "keyFiles", *flSSHKeyFiles, "useKnownHosts", *flSSHKnownHosts, "knownHostsFile", *flSSHKnownHostsFile)
@@ -883,7 +870,20 @@ func main() {
 	refreshCreds := func(ctx context.Context) error {
 		// These should all be mutually-exclusive configs.
 		for _, cred := range *flCredentials {
-			if err := git.StoreCredentials(ctx, cred.URL, cred.Username, cred.Password); err != nil {
+			password := cred.Password
+
+			// If this credential has a password file, re-read it from disk
+			// to pick up token rotation
+			if cred.PasswordFile != "" {
+				passwordFileBytes, err := os.ReadFile(cred.PasswordFile)
+				if err != nil {
+					return fmt.Errorf("can't read password file %q: %w", cred.PasswordFile, err)
+				}
+				password = string(passwordFileBytes)
+				git.log.V(3).Info("read password from file", "file", cred.PasswordFile)
+			}
+
+			if err := git.StoreCredentials(ctx, cred.URL, cred.Username, password); err != nil {
 				return err
 			}
 		}
@@ -2584,7 +2584,10 @@ OPTIONS
     --password-file <string>, $GITSYNC_PASSWORD_FILE
             The file from which the password or personal access token (see
             github docs) to use for git authentication (see --username) will be
-            read.  See also $GITSYNC_PASSWORD.
+            read.  The file is re-read before each sync attempt, allowing
+            git-sync to pick up token rotations automatically (e.g. when using
+            dynamic credentials from an external secrets system).
+            See also $GITSYNC_PASSWORD.
 
     --period <duration>, $GITSYNC_PERIOD
             How long to wait between sync attempts.  This must be at least

test_e2e.sh

@@ -2022,6 +2022,64 @@ function e2e::auth_http_password_file() {
     assert_file_eq "$ROOT/link/file" "${FUNCNAME[0]}"
 }
 
+##############################################
+# Test password-file reload on each sync
+##############################################
+function e2e::auth_password_file_reload() {
+    # Run a git-over-HTTP server.
+    local ctr
+    ctr=$(docker_run \
+        -v "$REPO":/git/repo:ro \
+        e2e/test/httpd)
+    local ip
+    ip=$(docker_ip "$ctr")
+
+    # Create a password file with the correct password.
+    echo -n "testpass" > "$WORK/password-file"
+
+    # First sync
+    echo "${FUNCNAME[0]} 1" > "$REPO/file"
+    git -C "$REPO" commit -qam "${FUNCNAME[0]} 1"
+
+    GIT_SYNC \
+        --period=1s \
+        --repo="http://$ip/repo" \
+        --root="$ROOT" \
+        --link="link" \
+        --username="testuser" \
+        --password-file="$WORK/password-file" \
+        --max-failures=100 \
+        &
+    wait_for_sync "${MAXWAIT}"
+    assert_link_exists "$ROOT/link"
+    assert_file_exists "$ROOT/link/file"
+    assert_file_eq "$ROOT/link/file" "${FUNCNAME[0]} 1"
+
+    # Change password file to wrong password
+    echo -n "wrong" > "$WORK/password-file.tmp"
+    mv "$WORK/password-file.tmp" "$WORK/password-file"
+
+    # Commit a change to the repo
+    echo "${FUNCNAME[0]} 2" > "$REPO/file"
+    git -C "$REPO" commit -qam "${FUNCNAME[0]} 2"
+
+    # Wait a bit and verify sync did NOT happen (still has old content)
+    sleep 3
+    assert_link_exists "$ROOT/link"
+    assert_file_exists "$ROOT/link/file"
+    assert_file_eq "$ROOT/link/file" "${FUNCNAME[0]} 1"
+
+    # Change password file back to correct password
+    echo -n "testpass" > "$WORK/password-file.tmp"
+    mv "$WORK/password-file.tmp" "$WORK/password-file"
+
+    # Verify sync now picks up the new change
+    wait_for_sync "${MAXWAIT}"
+    assert_link_exists "$ROOT/link"
+    assert_file_exists "$ROOT/link/file"
+    assert_file_eq "$ROOT/link/file" "${FUNCNAME[0]} 2"
+}
+
 ##############################################
 # Test SSH (user@host:path syntax)
 ##############################################