Require fee extension when registering domain in EAP

Failing to use the fee extension during EAP can result in charges to registrars
that are radically different than what they may have been expecting.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177597883

java/google/registry/flows/domain/DomainFlowUtils.java

@@ -631,6 +631,9 @@ public class DomainFlowUtils {
     // This only happens when the total fees are non-zero and include custom fees requiring the
     // extension.
     if (feeCommand == null) {
+      if (!feesAndCredits.getEapCost().isZero()) {
+        throw new FeesRequiredDuringEarlyAccessProgramException(feesAndCredits.getEapCost());
+      }
       if (feesAndCredits.getTotalCost().isZero() || !feesAndCredits.isFeeExtensionRequired()) {
         return;
       }
@@ -1167,9 +1170,6 @@ public class DomainFlowUtils {
 
   /** Fees must be explicitly acknowledged when performing an operation which is not free. */
   static class FeesRequiredForNonFreeOperationException extends RequiredParameterMissingException {
-    FeesRequiredForNonFreeOperationException() {
-      super("Fees must be explicitly acknowledged when performing an operation which is not free.");
-    }
 
     public FeesRequiredForNonFreeOperationException(Money expectedFee) {
       super(
@@ -1179,6 +1179,18 @@ public class DomainFlowUtils {
     }
   }
 
+  /** Fees must be explicitly acknowledged when creating domains during the Early Access Program. */
+  static class FeesRequiredDuringEarlyAccessProgramException
+      extends RequiredParameterMissingException {
+
+    public FeesRequiredDuringEarlyAccessProgramException(Money expectedFee) {
+      super(
+          "Fees must be explicitly acknowledged when creating domains "
+              + "during the Early Access Program. The EAP fee is: "
+              + expectedFee);
+    }
+  }
+
   /** The 'grace-period', 'applied' and 'refundable' fields are disallowed by server policy. */
   static class UnsupportedFeeAttributeException extends UnimplementedOptionException {
     UnsupportedFeeAttributeException() {