serverless-application-model: Unable to set authorizer on AWS::Serverless::HttpApi on $default path

Description:

Unable to set OAuth2 authorizer on API method [x-amazon-apigateway-any-method] for path [$default]

Steps to reproduce:

Below is template.Yaml file used and when run sam deploy gives errror as

Waiting for changeset to be created… “Error: Failed to create changeset for the stack: finapi, ex: Waiter ChangeSetCreateComplete failed: Waiter encountered a terminal failure state Status: FAILED. Reason: Transform AWS::Serverless-2016-10-31 failed with: Invalid Serverless Application Specification document. Number of errors found: 1. Resource with id [XXX] is invalid. Event with id [HttpApiEvent] is invalid. Unable to set Authorizer [MyOauth2Authorizer] on API method [x-amazon-apigateway-any-method] for path [$default] because the related API does not define any Authorizers.”

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Parameters:
  StageName:
    Type: String
    Default: Prod
Description: XXX

Globals:
  Api:
    EndpointConfiguration: REGIONAL
  Function:
    Timeout: 180


Resources:
  Api:
    Type: AWS::Serverless::HttpApi
    Properties:
      StageName: !Ref StageName
      Auth:
        Authorizers:
          MyOauth2Authorizer:
            IdentitySource: $request.header.Authorization
            JwtConfiguration:
              audience:
                - https://aws-api-gateway
              issuer: "https://xxxx.eu.auth0.com/"
        DefaultAuthorizer: MyOauth2Authorizer

  FinApiFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: com.StreamLambdaHandler::handleRequest
      Runtime: java11
      CodeUri: api
      MemorySize: 2048
      Environment: # More info about Env Vars: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#environment-object
        Variables:
          PARAM1: VALUE
      Events:
        HttpApiEvent:
          Type: HttpApi
          Properties:
            TimeoutInMillis: 20000
            PayloadFormatVersion: '2.0'
            Auth:
              Authorizer: MyOauth2Authorizer

Outputs:
  FApiFunctionApi:
    Description: URL for application
    Value: !Sub 'https://${ServerlessHttpApi}.execute-api.${AWS::Region}.amazonaws.com/pets'
    Export:
      Name: FApiFunctionApi

Observed result:

Waiting for changeset to be created… Error: Failed to create changeset for the stack: finapi, ex: Waiter ChangeSetCreateComplete failed: Waiter encountered a terminal failure state Status: FAILED. Reason: Transform AWS::Serverless-2016-10-31 failed with: Invalid Serverless Application Specification document. Number of errors found: 1. Resource with id [FinApiFunction] is invalid. Event with id [HttpApiEvent] is invalid. Unable to set Authorizer [MyOauth2Authorizer] on API method [x-amazon-apigateway-any-method] for path [$default] because the related API does not define any Authorizers.

Expected result:

function with API method [x-amazon-apigateway-any-method] for path [$default] is created on API gateway with OAuth 2.0/JWT authorizer configured

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: Ubuntu
2. sam --version: 1.15.0

Add --debug flag to command you are running