回答我自己的问题。这是将SQS作为服务代理集成到API网关中的方法：

To answer my own question. Here is how you integrate SQS as a Service Proxy in API Gateway:

PostMethod:
    Type: "AWS::ApiGateway::Method"
    Properties:
      AuthorizationType: "NONE"
      ApiKeyRequired: "true"
      HttpMethod: "POST"
      ResourceId: !Ref "SomeResource"
      RestApiId: !Ref "RestApi"
      MethodResponses:
      - StatusCode: 200
      Integration:
        Credentials: !GetAtt "RestApiRole.Arn"
        IntegrationHttpMethod: "POST"
        IntegrationResponses:
        - StatusCode: 200
        Type: "AWS"
        Uri: !Sub "arn:aws:apigateway:${AWS::Region}:sqs:action/SendMessage"
        RequestParameters:
          integration.request.querystring.QueueUrl: !Sub "'${SomeQueue}'"
          integration.request.querystring.MessageBody: "method.request.body"

我终于在各种文档中找到了所有问题的答案。我猜是RTFM。

I've finally found all answers to my questions in various documentation. RTFM I guess.

编辑：

，这里是RestApiRole的代码：

and here the code for RestApiRole:

RestApiRole:
    Type: "AWS::IAM::Role"
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
        - Action:
          - "sts:AssumeRole"
          Principal:
            Service:
            - "apigateway.amazonaws.com"
          Effect: "Allow"
      Policies:
      - PolicyName: "InvokeLambda"
        PolicyDocument:
          Version: "2012-10-17"
          Statement:
          - Action:
            - "lambda:InvokeFunction"
            Resource: !GetAtt "LambdaFunction.Arn"
            Effect: "Allow"