Add secrets directory credential resolver

internal/app/backends_test.go

@@ -131,6 +131,26 @@ func TestBackendFactoryRejectsUnsupportedDestination(t *testing.T) {
 	}
 }
 
+func TestBackendFactoryResolvesCredentialsThroughEnvironment(t *testing.T) {
+	factory := newBackendFactoryWithEnvironment(config.NewEnvironment(map[string]string{
+		"ACCESS_KEY_ID":     "secret-access",
+		"SECRET_ACCESS_KEY": "secret-secret",
+	}, func(string) (string, bool) {
+		return "", false
+	}))
+
+	creds, err := factory.resolveCredentials(config.Credentials{
+		AccessKeyIDEnv:     "ACCESS_KEY_ID",
+		SecretAccessKeyEnv: "SECRET_ACCESS_KEY",
+	})
+	if err != nil {
+		t.Fatalf("resolveCredentials() error = %v", err)
+	}
+	if creds.AccessKeyID != "secret-access" || creds.SecretAccessKey != "secret-secret" {
+		t.Fatalf("resolved credentials = %#v", creds)
+	}
+}
+
 func TestBackendFactoryBuildsSSHSourceOpenConfig(t *testing.T) {
 	cfg := sourceOpenConfig(config.Backend{
 		Backend: config.BackendSSH,