Check for an empty/null allocation token (#489)

* Check for an empty/null allocation token

In addition, we should be returning an authorization exception for an
invalid token, not a parameter syntax exception. See https://tools.ietf.org/html/draft-ietf-regext-allocation-token-04#section-2.1

* Add comment

core/src/main/java/google/registry/flows/domain/token/AllocationTokenFlowUtils.java

@@ -17,6 +17,7 @@ package google.registry.flows.domain.token;
 import static com.google.common.base.Preconditions.checkArgument;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Maps;
@@ -24,7 +25,7 @@ import com.google.common.net.InternetDomainName;
 import com.googlecode.objectify.Key;
 import google.registry.flows.EppException;
 import google.registry.flows.EppException.AssociationProhibitsOperationException;
-import google.registry.flows.EppException.ParameterValueSyntaxErrorException;
+import google.registry.flows.EppException.AuthorizationErrorException;
 import google.registry.flows.EppException.StatusProhibitsOperationException;
 import google.registry.model.domain.DomainCommand;
 import google.registry.model.domain.token.AllocationToken;
@@ -137,6 +138,12 @@ public class AllocationTokenFlowUtils {
 
   /** Loads a given token and validates that it is not redeemed */
   private AllocationToken loadToken(String token) throws EppException {
+    if (Strings.isNullOrEmpty(token)) {
+      // We load the token directly from the input XML. If it's null or empty we should throw
+      // an InvalidAllocationTokenException before the Datastore load attempt fails.
+      // See https://tools.ietf.org/html/draft-ietf-regext-allocation-token-04#section-2.1
+      throw new InvalidAllocationTokenException();
+    }
     AllocationToken tokenEntity = ofy().load().key(Key.create(AllocationToken.class, token)).now();
     if (tokenEntity == null) {
       throw new InvalidAllocationTokenException();
@@ -181,7 +188,7 @@ public class AllocationTokenFlowUtils {
   }
 
   /** The allocation token is invalid. */
-  public static class InvalidAllocationTokenException extends ParameterValueSyntaxErrorException {
+  public static class InvalidAllocationTokenException extends AuthorizationErrorException {
     public InvalidAllocationTokenException() {
       super("The allocation token is invalid");
     }

core/src/test/java/google/registry/flows/domain/token/AllocationTokenFlowUtilsTest.java

@@ -90,6 +90,22 @@ public class AllocationTokenFlowUtilsTest extends ShardableTestCase {
     assertValidateThrowsEppException(InvalidAllocationTokenException.class);
   }
 
+  @Test
+  public void test_validateToken_failsOnNullToken() {
+    assertAboutEppExceptions()
+        .that(
+            assertThrows(
+                InvalidAllocationTokenException.class,
+                () ->
+                    flowUtils.loadTokenAndValidateDomainCreate(
+                        createCommand("blah.tld"),
+                        null,
+                        Registry.get("tld"),
+                        "TheRegistrar",
+                        DateTime.now(UTC))))
+        .marshalsToXml();
+  }
+
   @Test
   public void test_validateToken_callsCustomLogic() {
     AllocationTokenFlowUtils failingFlowUtils =

docs/flows.md

@@ -324,7 +324,6 @@ An EPP flow that creates a new domain resource.
     *   The checksum in the specified TCNID does not validate.
     *   Domain name is under tld which doesn't exist.
 *   2005
-    *   The allocation token is invalid.
     *   Domain name must have exactly one part above the TLD.
     *   Domain name must not equal an existing multi-part TLD.
     *   The requested fee is expressed in a scale that is invalid for the given
@@ -337,6 +336,7 @@ An EPP flow that creates a new domain resource.
 *   2103
     *   Specified extension is not implemented.
 *   2201
+    *   The allocation token is invalid.
     *   Only a tool can pass a metadata extension.
     *   Registrar is not authorized to access this TLD.
     *   Registrar must be active in order to perform this operation.