x-amazon-apigateway-integration 为 uri 属性获取 lambda arn

Question

所述的x亚马逊apigateway-intregration扩展具有URI属性，可以取后端的ARN值。当我尝试使用 SAM 部署它时，出现以下错误

由于路径 /auth/signIn 中的集成格式错误，无法解析 API 定义

如何获取模板中指定的 lambda 函数的 ARN 值？

模板：

"api" : {
    "Type" : "AWS::Serverless::Api",
    "Properties" : {
        "StageName" : "prod",
        "DefinitionUri" : "src/api/swagger.json"
    }
},
"signIn": {
    "Type": "AWS::Serverless::Function",
    "Properties": {
        "Handler": "index.signIn",
        "Runtime": "nodejs8.10",
        "CodeUri": "./src",
        "FunctionName": "signIn",
        "ReservedConcurrentExecutions": 15,
        "Timeout": 5,
        "Events": {
            "SignIn": {
                "Type": "Api",
                "Properties": {
                    "Path": "/signIn",
                    "Method": "post",
                    "RestApiId" : {
                        "Ref": "api"
                    }
                }
            }
        }
    }
},

招摇定义：

"paths" : {
"/auth/signIn" : {
    "post" : {
        "x-amazon-apigateway-integration" : {
            "httpMethod" : "POST",
            "type" : "aws_proxy",
            "uri" : {
                "Fn::Sub" : {
                    "Fn::GetAtt": [
                    "signIn",
                    "Arn"
                ]}
            }
        },
        "parameters" : [
            {
                "name" : "email",
                "in" : "body",
                "required" : "true",
                "schema" : {
                    "type" : "string"
                }
            },
            {
                "name" : "password",
                "in" : "body",
                "required" : "true",
                "schema" : {
                    "type" : "string"
                }
            }
        ],
        "responses" : {
            "200" : {
                "description" : "Authenticated"
            },
            "default" : {
                "description" : "Unexpected Error"
            }
        }
    }
},