Creating a Frontend Custom Authorizer

Creating a Function for Frontend Custom Authentication

You need to create a FunctionGraph function for frontend custom authentication and define the required authentication information in the function.

1. Create a function in FunctionGraph.
   The function code must meet the following requirements (Python 2.7 is used as an example):

   • The function code has defined three types of request parameters in the following formats:
     • Header parameters: event["headers"]["Parameter name"]
     • Query string: event["queryStringParameters"]["Parameter name"]
     • Custom user data: event["user_data"]
   • The three types of request parameters obtained by the function are mapped to the custom authentication parameters defined in APIG.
     • Header parameter: Corresponds to the identity source specified in Header for custom authentication. The parameter value is transferred when the API that uses custom authentication is called.
     • Query string: Corresponds to the identity source specified in Query for custom authentication. The parameter value is transferred when the API that uses custom authentication is called.
     • Custom user data: Corresponds to the user data for custom authentication. The parameter value is specified when the custom authorizer is created.
   • The response of the function cannot be greater than 1 MB and must be displayed in the following format:

     {
         "statusCode":200,
         "body": "{\"status\": \"allow\", \"context\": {\"user\": \"abc\"}}"
     }

     The body field is a character string, which is JSON-decoded as follows:

     {
     	"status": "allow/deny",
     	"context": {
     		"user": "abc"
     	}
     }

     • The statusCode field is mandatory. If FunctionGraph is running properly and the code of the function complies with specifications, the value of statusCode is the response code of the function.
       • If response code is not 200, APIG considers that the function is abnormal and returns error code 500 and error information Internal server error.
       • When the relaxed mode of the custom authorizer is turned on and the function fails to connect or returns a 500 or 503 code, the authorizer does not check the status field in the body field. Instead, it will immediately return a message indicating that the API was successfully invoked. And the context field obtained from the function code will be empty.
     • The status field is mandatory and is used to identify the authentication result. The authentication result can only be allow or deny. allow indicates that the authentication is successful, and deny indicates that the authentication fails.
     • The context field is optional. It can be key-value pairs, but the key value cannot be a JSON object or an array. If the gateway supports the authorizer_context_support_num_bool feature, the key value can be a number or a Boolean value.

       The context field contains custom user data. After successful authentication, the user data is mapped to the backend parameters. The parameter name in context is case-sensitive and must be the same as the system parameter name. The parameter name must start with a letter and can contain 1 to 32 characters, including letters, digits, hyphens (-), and underscores (_).

       After successful frontend authentication, the value abc of user in context is mapped to the test parameter in the Header location of backend requests.

   Example header parameters:

   # -*- coding:utf-8 -*-
   import json
   def handler(event, context):
       if event["headers"].get("test")=='abc':
           resp = {
               'statusCode': 200,
               'body': json.dumps({
                   "status":"allow",
                   "context":{
                       "user":"abcd"
                   }
               })
           }
       else:
           resp = {
               'statusCode': 200,
               'body': json.dumps({
                   "status":"deny",
               })   
           }
       return json.dumps(resp)

   Example query parameters:

   # -*- coding:utf-8 -*-
   import json
   def handler(event, context):
       if event["queryStringParameters"].get("test")=='abc':
           resp = {
               'statusCode': 200,
               'body': json.dumps({
                   "status":"allow",
                   "context":{
                       "user":"abcd"
                   }
               })
           }
       else:
           resp = {
               'statusCode': 200,
               'body': json.dumps({
                   "status":"deny",
               })   
           }
       return json.dumps(resp)

   Example user data:

   # -*- coding:utf-8 -*-
   import json
   def handler(event, context):
       if event.get("user_data")=='abc':
           resp = {
               'statusCode': 200,
               'body': json.dumps({
                   "status":"allow",
                   "context":{
                       "user":"abcd"
                   }
               })
           }
       else:
           resp = {
               'statusCode': 200,
               'body': json.dumps({
                   "status":"deny",
               })   
           }
       return json.dumps(resp)

2. Test the function. In the Configure Test Event dialog box, select apig-event-template, edit the test event, and click Save. Then click Test.

   If the execution result is Success, the test is successful.

   Next, go to the APIG console to create a frontend custom authorizer.

   

Creating a Frontend Custom Authorizer

Before creating a frontend custom authorizer, ensure that the function backend used for frontend custom authentication has been created. Otherwise, create a function backend first. For details, see Creating a Function for Frontend Custom Authentication.

1. Go to the APIG console.
2. Select a dedicated gateway at the top of the navigation pane.

3. In the navigation pane, choose API Management > API Policies.
4. On the Custom Authorizers page, click Create Custom Authorizer.
   Configure custom authorizer parameters.

   Table 1 Parameters for creating a custom authorizer

   Parameter	Description
   Name	Authorizer name.
   Type	Select Frontend.
   Function URN	Select a function backend for frontend custom authentication. Only function backends in the Deployed state can be selected.
   Version/Alias	Select a function version or alias. For details, see FunctionGraph User Guide.
   Max. Cache Age (s)	The time for caching authentication results. The value ranges from 0s to 3,600s. 0 indicates that authentication results will not be cached.
   Relaxed Mode	When this option is enabled, APIG accepts client requests even when FunctionGraph cannot connect or returns an error code starting with "5". If there is a retry request, the last returned result is used. When this option is enabled, if a custom authorizer is used for backend authentication of an API, the value of the backend authentication parameter is empty. The relaxed mode has security risks. Therefore, exercise caution when selecting this mode.
   Identity Sources	Request parameters used for authentication. This parameter is mandatory only if Max. Cache Age (s) is greater than 0. When the cache is used, this parameter is used as a search criterion to query authentication results.
   Send Request Body	Determine whether to send the body of each API request to the authentication function. If you enable this option, the request body will be sent to the authentication function in the same way as the headers and query strings.
   User Data	Customized request parameters to be used together with Identity Sources when APIG invokes a function.

5. Click OK.