Read the error response body when the auth endpoint returns an error status

src/main/java/com/pusher/client/util/BaseHttpAuthClient.java

@@ -134,18 +134,26 @@ protected String performAuthRequest() {
             wr.flush();
             wr.close();
 
-            // Read response
-            final InputStream is = connection.getInputStream();
-            final BufferedReader rd = new BufferedReader(new InputStreamReader(is));
-            String line;
+            // Read response. For error statuses, getInputStream() throws, so the
+            // body the server sent is read from the error stream instead.
+            final int responseHttpStatus = connection.getResponseCode();
+            final InputStream is = responseHttpStatus >= HttpURLConnection.HTTP_BAD_REQUEST
+                    ? connection.getErrorStream()
+                    : connection.getInputStream();
             final StringBuilder response = new StringBuilder();
-            while ((line = rd.readLine()) != null) {
-                response.append(line);
+            if (is != null) {
+                final BufferedReader rd = new BufferedReader(new InputStreamReader(is));
+                String line;
+                while ((line = rd.readLine()) != null) {
+                    response.append(line);
+                }
+                rd.close();
             }
-            rd.close();
 
-            final int responseHttpStatus = connection.getResponseCode();
             if (responseHttpStatus != 200 && responseHttpStatus != 201) {
+                if (response.length() == 0) {
+                    throw authFailureException("Server returned HTTP response code: " + responseHttpStatus);
+                }
                 throw authFailureException(response.toString());
             }
 

src/test/java/com/pusher/client/util/HttpChannelAuthorizerTest.java

@@ -1,12 +1,22 @@
 package com.pusher.client.util;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import com.pusher.client.AuthorizationFailureException;
 
+import com.sun.net.httpserver.HttpServer;
+
 import org.junit.Test;
 
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+
 public class HttpChannelAuthorizerTest {
 
     @Test(expected = IllegalArgumentException.class)
@@ -31,4 +41,26 @@ public void testNon200ResponseThrowsAuthorizationFailureException() {
         final HttpChannelAuthorizer auth = new HttpChannelAuthorizer("https://127.0.0.1/no-way-this-is-a-valid-url");
         auth.authorize("private-fish", "some socket id");
     }
+
+    @Test
+    public void testErrorResponseBodyIsUsedAsAuthorizationFailureMessage() throws IOException {
+        final byte[] errorBody = "{\"error\":\"forbidden\"}".getBytes(StandardCharsets.UTF_8);
+        final HttpServer server = HttpServer.create(new InetSocketAddress(InetAddress.getLoopbackAddress(), 0), 0);
+        server.createContext("/auth", exchange -> {
+            exchange.sendResponseHeaders(403, errorBody.length);
+            try (OutputStream os = exchange.getResponseBody()) {
+                os.write(errorBody);
+            }
+        });
+        server.start();
+        try {
+            final HttpChannelAuthorizer auth = new HttpChannelAuthorizer("http://127.0.0.1:" + server.getAddress().getPort() + "/auth");
+            auth.authorize("private-fish", "some socket id");
+            fail("Expected AuthorizationFailureException");
+        } catch (final AuthorizationFailureException e) {
+            assertEquals("{\"error\":\"forbidden\"}", e.getMessage());
+        } finally {
+            server.stop(0);
+        }
+    }
 }

src/test/java/com/pusher/client/util/HttpUserAuthenticatorTest.java

@@ -1,12 +1,22 @@
 package com.pusher.client.util;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import com.pusher.client.AuthenticationFailureException;
 
+import com.sun.net.httpserver.HttpServer;
+
 import org.junit.Test;
 
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+
 public class HttpUserAuthenticatorTest {
 
     @Test(expected = IllegalArgumentException.class)
@@ -31,4 +41,26 @@ public void testNon200ResponseThrowsAuthenticationFailtureException() {
         final HttpUserAuthenticator auth = new HttpUserAuthenticator("https://127.0.0.1/no-way-this-is-a-valid-url");
         auth.authenticate("some socket id");
     }
+
+    @Test
+    public void testErrorResponseBodyIsUsedAsAuthenticationFailureMessage() throws IOException {
+        final byte[] errorBody = "{\"error\":\"forbidden\"}".getBytes(StandardCharsets.UTF_8);
+        final HttpServer server = HttpServer.create(new InetSocketAddress(InetAddress.getLoopbackAddress(), 0), 0);
+        server.createContext("/auth", exchange -> {
+            exchange.sendResponseHeaders(403, errorBody.length);
+            try (OutputStream os = exchange.getResponseBody()) {
+                os.write(errorBody);
+            }
+        });
+        server.start();
+        try {
+            final HttpUserAuthenticator auth = new HttpUserAuthenticator("http://127.0.0.1:" + server.getAddress().getPort() + "/auth");
+            auth.authenticate("some socket id");
+            fail("Expected AuthenticationFailureException");
+        } catch (final AuthenticationFailureException e) {
+            assertEquals("{\"error\":\"forbidden\"}", e.getMessage());
+        } finally {
+            server.stop(0);
+        }
+    }
 }