在 API Gateway 集成请求的设置中，可以将 Content-Type 映射为 text/plain。在这种情况下，最好将映射值设置为字符串 "*"，以确保 AWS API Gateway 不会将 Content-Type 转换为其他 MIME 类型。以下是示例代码：

const integration = new apigateway.MockIntegration({
  requestTemplates: {
    'application/json': '{\n "statusCode": 200\n}'
  },
  integrationResponses: [
    {
      statusCode: "200",
      responseTemplates: {
        'text/plain': '$input.path("$.mockResponse")'
      },
      responseParameters: {
        'method.response.header.Content-Type': "'text/plain'"
      }
    }
  ],
  passthroughBehavior: apigateway.PassthroughBehavior.NEVER,
  requestParameters: {}
});

const method = api.root.addResource('test').addMethod('GET', integration);
method.methodResponses.push({
  statusCode: '200',
  responseParameters: {
    'method.response.header.Content-Type': true,
  },
  responseModels: {
    'text/plain': new apigateway.EmptyModel()
  }
});