feat(auth): allow JWT IP changes by configuration (#1236)

* feat(auth): allow JWT IP changes by configuration

* fix(auth): make JWT IP change setting concurrency-safe

* test(auth): move JWT IP change setting tests out of MCP test file

model/jwt_ip_change_atomic_test.go

@@ -0,0 +1,56 @@
+package model
+
+import (
+	"path/filepath"
+	"sync"
+	"testing"
+)
+
+func TestJWTIPChangeAllowedPersistence(t *testing.T) {
+	c := &Config{}
+	if c.JWTIPChangeAllowed() {
+		t.Fatal("zero-value Config must bind JWT sessions to their IP")
+	}
+	// An absent agent secret makes Read save the config during initialization.
+	path := newTempConfig(t, "jwt_secret_key: test\nallow_jwt_ip_change: true\n")
+	if err := c.Read(path, nil); err != nil {
+		t.Fatal(err)
+	}
+	if !c.JWTIPChangeAllowed() {
+		t.Fatal("Read must initialize the atomic mirror before saving")
+	}
+	for _, want := range []bool{true, false} {
+		c.SetJWTIPChangeAllowed(want)
+		if err := c.Save(); err != nil {
+			t.Fatal(err)
+		}
+		reloaded := &Config{}
+		if err := reloaded.Read(path, nil); err != nil {
+			t.Fatal(err)
+		}
+		if c.AllowJWTIPChange != want || reloaded.JWTIPChangeAllowed() != want {
+			t.Fatalf("saved and reloaded setting must be %v", want)
+		}
+	}
+}
+
+func TestJWTIPChangeAllowedConcurrentAccess(t *testing.T) {
+	c := &Config{filePath: filepath.Join(t.TempDir(), "config.yaml")}
+	var wg sync.WaitGroup
+	wg.Go(func() {
+		for i := 0; i < 10000; i++ {
+			c.SetJWTIPChangeAllowed(i%2 == 0)
+		}
+	})
+	wg.Go(func() {
+		for i := 0; i < 10000; i++ {
+			_ = c.JWTIPChangeAllowed()
+		}
+	})
+	for i := 0; i < 20; i++ {
+		if err := c.Save(); err != nil {
+			t.Error(err)
+		}
+	}
+	wg.Wait()
+}