Fix format of header list in OAuth2ServiceException message

token-client/src/main/java/com/sap/cloud/security/xsuaa/client/OAuth2ServiceException.java

@@ -9,6 +9,7 @@
 import java.io.Serial;
 import java.net.URI;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
 import java.util.stream.Collectors;
@@ -120,16 +121,11 @@ public Builder withResponseBody(String responseBody) {
 		}
 
 		public Builder withHeaders(String... headers) {
-			StringBuilder sb = new StringBuilder();
-			sb.append("[");
-			for (String header : headers) {
-				if (header != null) {
-					this.headers.add(header);
-				}
-				sb.append(header);
-			}
-			sb.append("]");
-			this.headersString = sb.toString();
+			List<String> headerList = Arrays.stream(headers).filter(Objects::nonNull).toList();
+
+			this.headers.addAll(headerList);
+			this.headersString = headerList.stream().collect(Collectors.joining(", ", "[", "]"));
+
 			return this;
 		}
 

token-client/src/test/java/com/sap/cloud/security/xsuaa/client/OAuth2ServiceExceptionTest.java

@@ -0,0 +1,33 @@
+package com.sap.cloud.security.xsuaa.client;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class OAuth2ServiceExceptionTest {
+    public static final String SERVICE_EXCEPTION = "Service Exception";
+    private static List<String> headers;
+    private static OAuth2ServiceException builtWithHeaders;
+    private static OAuth2ServiceException createdWithHeaders;
+
+    @BeforeAll
+    static void setup() {
+        headers = List.of("header1", "header2");
+        builtWithHeaders = OAuth2ServiceException.builder(SERVICE_EXCEPTION).withHeaders(headers.toArray(String[]::new)).build();
+        createdWithHeaders = new OAuth2ServiceException(SERVICE_EXCEPTION, 400, headers);
+    }
+
+    @Test
+    void testWithHeaders() {
+        assertIterableEquals(headers, builtWithHeaders.getHeaders());
+        assertTrue(builtWithHeaders.getMessage().contains(SERVICE_EXCEPTION));
+        assertTrue(builtWithHeaders.getMessage().contains("[header1, header2]"));
+
+        assertIterableEquals(headers, createdWithHeaders.getHeaders());
+        assertTrue(createdWithHeaders.getMessage().contains(SERVICE_EXCEPTION));
+        assertFalse(createdWithHeaders.getMessage().contains("[header1, header2]"));
+    }
+}