Unable to determine service/operation name to be authorized

解決策

IntegrationHttpMethodをPOSTにする

    "MockMethod": {
      "Type": "AWS::ApiGateway::Method",
      "Properties": {
        "ApiKeyRequired" : "false",
        "AuthorizationType": "NONE",
        "HttpMethod": "GET",
        "Integration": {
          "IntegrationHttpMethod" : "POST",
          "Type": "AWS",
          "Uri" : {"Fn::Join" : ["", [
            "arn:aws:apigateway:",
            { "Ref" : "AWS::Region" },
            ":lambda:path/2015-03-31/functions/",
            {"Ref" : "LambdaFunctionArn" },
            "/invocations"
          ]]}
        },
        "ResourceId": { "Fn::GetAtt": ["RestApi", "RootResourceId"] },
        "RestApiId": { "Ref": "RestApi" }
      },
      "DependsOn" : "RestApi"
    }

https://forums.aws.amazon.com/thread.jspa?threadID=209420