title: Syntax for submitting a mutation to a graphql-relay mutationWithClientMutationId
body: <p>I defined a GraphQL Mutation using graphql-relay but am having issues figuring out how to submit a mutation to it.</p>
  
  <p>Here is the relevant schema:</p>
  
  <pre><code>const userType = new GraphQLObjectType({
    name: 'User',
    description: 'user',
    fields: () =&gt; ({
      id: {
        type: new GraphQLNonNull(GraphQLString),
        description: 'The UUID for the user.',
        resolve(user) {
          return user.uuid;
        },
      },
    })
  });
  
  const registerUser = mutationWithClientMutationId({
    name: 'registerUser',
    inputFields: {
    },
    outputFields: {
      user: {
        type: userType,
        resolve: (payload) =&gt; {
          models.user.findById(payload.userId);
        }
      },
    },
    mutateAndGetPayload: (args) =&gt; {
      var newUser = models.user.build().save();
      return {
        userId: newUser.id,
      };
    }
  });
  
  
  const rootMutation = new GraphQLObjectType({
    name: 'RootMutationType',
    fields: {
      registerUser: registerUser,
    },
  });
  
  const schema = new GraphQLSchema({
    query: rootQuery,
    mutation: rootMutation,
  });
  </code></pre>
  
  <p>What should an HTTP call look like to register a new user and get back the  userId?</p>
  
  <p>Thanks!</p>