AWS CloudFormation template example for allowing uploading files to S3 via API Gateway

api-gw-template.yml

AWSTemplateFormatVersion: '2010-09-09'
Parameters:
  ApiGatewayStack:
    Description: The stack where the api gateway rest api is defined
    Type: String
    Default: dev-maat-apigw-app
  EventBucket:
    Type: String
    Default: dev-maat-bucket
  CorsAllowOrigin:
    Type: String
    Default: '*'

Resources:
  # Resource: /maat
  MaatResource:
    Type: AWS::ApiGateway::Resource
    Properties:
      RestApiId:
        Fn::ImportValue: !Sub ${ApiGatewayStack}::AppApiGw
      ParentId:
        Fn::ImportValue: !Sub ${ApiGatewayStack}::AppApiGwRootResourceId
      PathPart: 'maat'
# Resource: /maat/input
  MaatInputResource:
    Type: AWS::ApiGateway::Resource
    Properties:
      RestApiId:
        Fn::ImportValue: !Sub ${ApiGatewayStack}::AppApiGw
      ParentId:
        Ref: WssiResource
      PathPart: 'input'
      
  MaatObjectPostRequest:
    Type: AWS::ApiGateway::Method
    Properties:
      AuthorizationType: NONE
      HttpMethod: POST
      RestApiId:
        Fn::ImportValue: !Sub ${ApiGatewayStack}::AppApiGw
      ResourceId:
        Ref: MaatInputResource
      Integration:
        Credentials: !GetAtt ApiGatewayS3ProxyRole.Arn
        IntegrationHttpMethod: PUT
        PassthroughBehavior: WHEN_NO_MATCH
        RequestParameters:
          integration.request.path.requestId: context.requestId
          integration.request.header.x-amz-server-side-encryption: "'AES256'"
        Type: AWS
        Uri: !Sub arn:aws:apigateway:${AWS::Region}:s3:path/${EventBucket}/input/{requestId}
        IntegrationResponses:
          - StatusCode: '201'
            ResponseParameters:
                method.response.header.Access-Control-Allow-Headers: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"
                method.response.header.Access-Control-Allow-Methods: "'GET,POST,OPTIONS'"
                method.response.header.Access-Control-Allow-Origin: !Sub "'${CorsAllowOrigin}'"
            ResponseTemplates:
                application/json: ''
      MethodResponses:
        - StatusCode: '201'
          ResponseParameters:
              method.response.header.Access-Control-Allow-Headers: true
              method.response.header.Access-Control-Allow-Methods: true
              method.response.header.Access-Control-Allow-Origin: true
  
  MaatObjectOptionsRequest:
    Type: AWS::ApiGateway::Method
    Properties:
      AuthorizationType: NONE
      HttpMethod: OPTIONS
      RestApiId:
        Fn::ImportValue: !Sub ${ApiGatewayStack}::AppApiGw
      ResourceId:
        Ref: MaatResource
      Integration:
        IntegrationResponses:
          - StatusCode: '200'
            ResponseParameters:
                method.response.header.Access-Control-Allow-Headers: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"
                method.response.header.Access-Control-Allow-Methods: "'GET,POST,OPTIONS'"
                method.response.header.Access-Control-Allow-Origin: !Sub "'${CorsAllowOrigin}'"
            ResponseTemplates:
                application/json: ''
        PassthroughBehavior: NEVER
        Type: MOCK
        RequestTemplates:
            application/json: '{"statusCode": 200}'
      MethodResponses:
        - StatusCode: '200'
          ResponseModels:
              application/json: Empty
          ResponseParameters:
              method.response.header.Access-Control-Allow-Headers: true
              method.response.header.Access-Control-Allow-Methods: true
              method.response.header.Access-Control-Allow-Origin: true
              
  ApiGatewayS3ProxyRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service:
                - apigateway.amazonaws.com
            Action:
              - sts:AssumeRole
      Policies:
        - PolicyName: s3
          PolicyDocument:
            Version: '2012-10-17'
            Statement:
              - Effect: Allow
                Action:
                  - s3:PutObject
                Resource:
                  - !Sub 'arn:aws:s3:::${EventBucket}'
                  - !Sub 'arn:aws:s3:::${EventBucket}/*'

Do you have the template that outputs {ApiGatewayStack}::AppApiGw and ${ApiGatewayStack}::AppApiGwRootResourceId ?