KEYCLOAK-18289: use utf-8 encoding for simplehttp (#8025)

Co-authored-by: Stian Thorgersen <stianst@gmail.com>

server-spi-private/src/main/java/org/keycloak/broker/provider/util/SimpleHttp.java

@@ -314,7 +314,7 @@ public class SimpleHttp {
             }
         }
 
-        return new UrlEncodedFormEntity(urlParameters);
+        return new UrlEncodedFormEntity(urlParameters, StandardCharsets.UTF_8);
     }
 
     public static class Response {

server-spi-private/src/test/java/org/keycloak/broker/provider/util/SimpleHttpTest.java

@@ -23,6 +23,7 @@ import org.junit.runners.Parameterized.Parameters;
 import org.keycloak.common.util.StreamUtil;
 
 import java.io.IOException;
+import java.net.URLEncoder;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
@@ -99,6 +100,13 @@ public final class SimpleHttpTest {
             assertEquals("{\"value\":\"" + value + "\"}", client.data);
         }
 
+        @Test
+        public void requestWithEncodingParam() throws IOException {
+            HttpClientMock client = new HttpClientMock();
+            SimpleHttp.doPost("", client).param("dummy", value).asResponse();
+            assertEquals("dummy=" + URLEncoder.encode(value, "UTF-8"), client.data);
+        }
+
         public static final class DummyEntity {
             public String value;
             public DummyEntity(String value) {