fix(refresh): honor userIdentifierClaim in token refresh path (#132)

patch-release

The refresh path in token_manager.go hardcoded the "email" claim when
extracting the user identifier from a refreshed ID token, ignoring the
configured userIdentifierClaim. Keycloak users without an email claim
(using sub or another identifier) were kicked out on refresh even
though their initial login worked.

The callback path (auth_flow.go:226-239) already honored
userIdentifierClaim with "sub" fallback; PR #100 (commit a316a98)
added that support but missed the refresh path.

Mirror the callback logic in refreshToken so both paths behave the same.

Cleanup: rename Get/SetEmail to Get/SetUserIdentifier on SessionData
to match the actual semantics. The slot already stored the configured
identifier (email, sub, oid, upn, preferred_username), only the API
name was misleading. Storage key "email" → "user_identifier" and
combinedSessionPayload field E (json:"e") → Ui (json:"ui").

Compat note: existing user sessions invalidate on upgrade — every active
user re-authenticates once after deploying this change.

session_behaviour_test.go

@@ -320,17 +320,16 @@ func (s *SessionBehaviourSuite) TestSessionData_DirtyTracking() {
 	s.False(session.IsDirty())
 }
 
-// TestSessionData_SetEmail tests email setter with dirty tracking
-func (s *SessionBehaviourSuite) TestSessionData_SetEmail() {
+// TestSessionData_SetUserIdentifier tests user identifier setter with dirty tracking
+func (s *SessionBehaviourSuite) TestSessionData_SetUserIdentifier() {
 	req := httptest.NewRequest(http.MethodGet, "/test", nil)
 
 	session, err := s.sessionManager.GetSession(req)
 	s.Require().NoError(err)
 	defer session.returnToPoolSafely()
 
-	// Set email
-	session.SetEmail("test@example.com")
-	s.Equal("test@example.com", session.GetEmail())
+	session.SetUserIdentifier("test@example.com")
+	s.Equal("test@example.com", session.GetUserIdentifier())
 	s.True(session.IsDirty())
 }
 
@@ -568,7 +567,7 @@ func (s *SessionBehaviourSuite) TestSessionData_Clear() {
 	// Set some data
 	err = session.SetAuthenticated(true)
 	s.Require().NoError(err)
-	session.SetEmail("test@example.com")
+	session.SetUserIdentifier("test@example.com")
 	session.SetCSRF("csrf-token")
 
 	// Clear session
@@ -588,7 +587,7 @@ func (s *SessionBehaviourSuite) TestSessionData_Save() {
 	defer session.returnToPoolSafely()
 
 	// Modify session
-	session.SetEmail("test@example.com")
+	session.SetUserIdentifier("test@example.com")
 	s.True(session.IsDirty())
 
 	// Save session