add custom command parts

this allows to set custom config cli arguments and add/overwrite default settings from the testcontainer assumptions

README.md

@@ -180,6 +180,19 @@ KeycloakContainer keycloak = new KeycloakContainer()
     .withFeaturesDisabled("authorization", "impersonation", "...");
 ```
 
+## Custom CLI Config arguments
+
+All default configurations in this Testcontainer is done through environment variables.
+You can overwrite and/or add config settings on command-line-level (cli args) with this method:
+
+```java
+@Container
+KeycloakContainer keycloak = new KeycloakContainer()
+    .withCustomCommand("--hostname=keycloak.local");
+```
+
+A warning will be printed to the log output when custom command parts are being used, so that you are aware that you are responsible on your own for proper execution of this container.
+
 ## Testing Custom Extensions
 
 To ease extension testing, you can tell the Keycloak Testcontainer to detect extensions in a given classpath folder.

src/main/java/dasniko/testcontainers/keycloak/ExtendableKeycloakContainer.java

@@ -109,6 +109,7 @@ public abstract class ExtendableKeycloakContainer<SELF extends ExtendableKeycloa
 
     private String providerClassLocation;
     private List<File> providerLibsLocations;
+    private List<String> customCommandParts;
 
     /**
      * Create a KeycloakContainer with default image and version tag
@@ -222,17 +223,33 @@ protected void configure() {
             }
         }
 
+        if (customCommandParts != null) {
+            logger().warn("You are using custom command parts. " +
+                "Container behavior and configuration may be corrupted. " +
+                "You are self responsible for proper behavior and functionality!\n" +
+                "CustomCommandParts: {}", customCommandParts);
+            commandParts.addAll(customCommandParts);
+        }
+
         setCommand(commandParts.toArray(new String[0]));
     }
 
     @Override
     public SELF withCommand(String cmd) {
-        throw new IllegalStateException("You are trying to set custom container commands, which is currently not supported by this Testcontainer.");
+        throw new IllegalStateException("You are trying to set custom container commands, which is not supported by this Testcontainer. Try using the withCustomCommand() method.");
     }
 
     @Override
     public SELF withCommand(String... commandParts) {
-        throw new IllegalStateException("You are trying to set custom container commands, which is currently not supported by this Testcontainer.");
+        throw new IllegalStateException("You are trying to set custom container commands, which is not supported by this Testcontainer. Try using the withCustomCommand() method.");
+    }
+
+    public SELF withCustomCommand(String cmd) {
+        if (customCommandParts == null) {
+            customCommandParts = new ArrayList<>();
+        }
+        customCommandParts.add(cmd);
+        return self();
     }
 
     /**

src/test/java/dasniko/testcontainers/keycloak/KeycloakContainerTest.java

@@ -1,5 +1,6 @@
 package dasniko.testcontainers.keycloak;
 
+import io.restassured.response.ValidatableResponse;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
@@ -16,6 +17,7 @@
 
 import static io.restassured.RestAssured.given;
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.endsWith;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.is;
@@ -118,9 +120,7 @@ public void shouldRunOnDifferentContextPath() {
             String authServerUrl = keycloak.getAuthServerUrl();
             assertThat(authServerUrl, endsWith(contextPath));
 
-            given().when().get(authServerUrl + "/realms/master/.well-known/openid-configuration")
-                .then().statusCode(200);
-
+            getWellKnownOpenidConfigurationResponse(authServerUrl);
             checkKeycloakContainerInternals(keycloak);
         }
     }
@@ -172,6 +172,20 @@ void shouldOpenFixedDebugPort() throws IOException {
         }
     }
 
+    @Test
+    void shouldUseCustomCommandPart() {
+        try (KeycloakContainer keycloak = new KeycloakContainer().withCustomCommand("--hostname=keycloak.local")) {
+            keycloak.start();
+            String issuer = getWellKnownOpenidConfigurationResponse(keycloak.getAuthServerUrl()).extract().path("issuer");
+            assertThat(issuer, containsString("keycloak.local"));
+        }
+    }
+
+    private static ValidatableResponse getWellKnownOpenidConfigurationResponse(String authServerUrl) {
+        return given().when().get(authServerUrl + "/realms/master/.well-known/openid-configuration")
+            .then().statusCode(200);
+    }
+
     private void checkKeycloakContainerInternals(KeycloakContainer keycloak) {
         Keycloak keycloakAdminClient = keycloak.getKeycloakAdminClient();
         ServerInfoRepresentation serverInfo = keycloakAdminClient.serverInfo().getInfo();