feat(sts): Add IsExpired helpers and use them in expiration tests

- Add Credentials.IsExpired() and SessionInfo.IsExpired() in new file session_helpers.go.
- Update TestSTSSessionClaimsToSessionInfoCredentialExpiration to use helpers for clearer intent.

weed/iam/sts/session_claims_test.go

@@ -179,11 +179,13 @@ func TestSTSSessionClaimsToSessionInfoCredentialExpiration(t *testing.T) {
 			assert.True(t, sessionInfo.Credentials.Expiration.Sub(tc.expiresAt) < time.Second)
 
 			// We set tc.expiresAt to past/future values to exercise expiration handling.
-			// Assert the credentials' expiration relative to now to exercise code behavior
+			// Use helper methods to assert expiration behavior on both SessionInfo and Credentials.
 			if tc.expectNotExpired {
-				assert.True(t, time.Now().Before(sessionInfo.Credentials.Expiration), tc.description)
+				assert.False(t, sessionInfo.IsExpired(), tc.description)
+				assert.False(t, sessionInfo.Credentials.IsExpired(), tc.description)
 			} else {
-				assert.True(t, time.Now().After(sessionInfo.Credentials.Expiration), tc.description)
+				assert.True(t, sessionInfo.IsExpired(), tc.description)
+				assert.True(t, sessionInfo.Credentials.IsExpired(), tc.description)
 			}
 		})
 	}

weed/iam/sts/session_helpers.go

@@ -0,0 +1,20 @@
+package sts
+
+import "time"
+
+// IsExpired returns true if the credentials have expired
+func (c *Credentials) IsExpired() bool {
+	if c == nil {
+		return true
+	}
+	return time.Now().After(c.Expiration)
+}
+
+// IsExpired returns true if the session has expired
+func (s *SessionInfo) IsExpired() bool {
+	// If SessionInfo is nil, consider it expired
+	if s == nil {
+		return true
+	}
+	return time.Now().After(s.ExpiresAt)
+}