Added config generate-csrf-key, to store a CSRF key that survives restarts and works across instances

Without server.csrf.tokens.key, each server process signs CSRF tokens with
a random key of its own, so tokens are lost on a restart and rejected by
other instances. "job-search config generate-csrf-key" stores a new random
32-byte hex key in the configuration file, without printing it. --print
only prints a key, for JOBSEARCH_SERVER_CSRF_TOKENS_KEY or another
instance. An existing key is only replaced with --force, as that
invalidates every issued token, and no key is stored while
JOBSEARCH_SERVER_CSRF_TOKENS_KEY is set, as it would override the file.

internal/cli/config/csrf_key_test.go

@@ -0,0 +1,104 @@
+package config
+
+import (
+	"encoding/hex"
+	"strings"
+	"testing"
+
+	"git.avsdev.uk/Go/job-search/internal/cli/cmdtest"
+)
+
+// fileCSRFKey returns the CSRF key in config.yaml, or "" if it has none.
+func fileCSRFKey(t *testing.T) string {
+	t.Helper()
+	key, _ := fileSettings(t, "config.yaml")[csrfKeySetting].(string)
+	return key
+}
+
+// checkCSRFKey fails the test unless key is csrfKeyBytes of hex.
+func checkCSRFKey(t *testing.T, key string) {
+	t.Helper()
+	decoded, err := hex.DecodeString(key)
+	if err != nil || len(decoded) != csrfKeyBytes {
+		t.Fatalf("key %q is not %d bytes of hex", key, csrfKeyBytes)
+	}
+}
+
+// The key is stored in the configuration file, without being printed, and
+// the file's other settings are kept.
+func TestGenerateCSRFKey(t *testing.T) {
+	cmdtest.Setup(t, appConfig)
+
+	out := mustRun(t, "config", "generate-csrf-key")
+	cmdtest.Contains(t, out, csrfKeySetting+" set in ")
+
+	key := fileCSRFKey(t)
+	checkCSRFKey(t, key)
+	if strings.Contains(out, key) {
+		t.Errorf("the key was printed: %s", out)
+	}
+	if fileSettings(t, "config.yaml")["sources.sleeper.interval"] != "2m" {
+		t.Errorf("other settings were changed: %v", fileSettings(t, "config.yaml"))
+	}
+}
+
+// An existing key is only replaced with --force.
+func TestGenerateCSRFKeyExisting(t *testing.T) {
+	cmdtest.Setup(t, appConfig)
+	mustRun(t, "config", "generate-csrf-key")
+	first := fileCSRFKey(t)
+
+	_, err := run(t, "config", "generate-csrf-key")
+	cmdtest.ErrContains(t, err, "already set: --force replaces it")
+	if fileCSRFKey(t) != first {
+		t.Fatal("the key was replaced without --force")
+	}
+
+	mustRun(t, "config", "generate-csrf-key", "--force")
+	second := fileCSRFKey(t)
+	checkCSRFKey(t, second)
+	if second == first {
+		t.Error("--force kept the same key")
+	}
+}
+
+// --print only prints a key, and needs no configuration file.
+func TestGenerateCSRFKeyPrint(t *testing.T) {
+	cmdtest.Setup(t, "")
+
+	key := strings.TrimSpace(mustRun(t, "config", "generate-csrf-key", "--print"))
+	checkCSRFKey(t, key)
+
+	other := strings.TrimSpace(mustRun(t, "config", "generate-csrf-key", "--print"))
+	if other == key {
+		t.Error("two keys were the same")
+	}
+}
+
+// A key in the environment variable would override the file, so none is
+// stored while it is set.
+func TestGenerateCSRFKeyEnvironment(t *testing.T) {
+	cmdtest.Setup(t, appConfig)
+	t.Setenv("JOBSEARCH_SERVER_CSRF_TOKENS_KEY", generateCSRFKey())
+
+	_, err := run(t, "config", "generate-csrf-key")
+	cmdtest.ErrContains(t, err, "JOBSEARCH_SERVER_CSRF_TOKENS_KEY is set")
+	if fileCSRFKey(t) != "" {
+		t.Error("a key was stored")
+	}
+}
+
+func TestGenerateCSRFKeyWithoutConfigFile(t *testing.T) {
+	cmdtest.Setup(t, "")
+	_, err := run(t, "config", "generate-csrf-key")
+	cmdtest.ErrContains(t, err, "no configuration file exists")
+}
+
+func TestGenerateCSRFKeyFlags(t *testing.T) {
+	cmdtest.Setup(t, appConfig)
+	_, err := run(t, "config", "generate-csrf-key", "--print", "--force")
+	cmdtest.ErrContains(t, err, "none of the others")
+	if _, err := run(t, "config", "generate-csrf-key", "extra"); err == nil {
+		t.Error("an argument was accepted")
+	}
+}