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This section introduces handlers and using an example, explains how to write a custom handler: 

Table of Contents

Introduction to Handlers

When an API is created, a file with its synapse configuration is added to the API Gateway. You can find it in the <APIM_HOME>/repository/deployment/server/synapse-configs/default/api folder. It has a set of handlers, each of which is executed on the APIs in the same order they appear in the configuration. You find the default handlers in any API's Synapse definition as shown below.

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  • APIAuthenticationHandler: Validates the OAuth2 bearer token used to invoke the API. It also determines whether the token is of type Production or Sandbox and sets MessageContext variables as appropriate. 
  • APIThrottleHandler: Throttles requests based on the throttling policy specified by the policyKey property. Throttling is applied both at the application level as well as subscription level.
  • APIMgtUsageHandler: Publishes events to BAM for collection and analysis of statistics. This handler only comes to effect if API usage tracking is enabled. See Publishing API Runtime Statistics for more information.
  • APIMgtGoogleAnalyticsTrackingHandler: Publishes events to Google Analytics. This handler only comes into effect if Google analytics tracking is enabled. See Integrating with Google Analytics for more information.
  • APIManagerExtensionHandler: Extends the mediation flow of messages passing through the API Gateway. See Adding Mediation Extensions for more information.

Writing a custom handler

Let's see how you can write a custom handler and apply it to the API Manager. In this example, we extend the authentication handler. 

WSO2 API Manager provides the OAuth2 bearer token as its default authentication mechanism. The source code of the implementation is here. Similarly, you can extend the API Manager to support any custom authentication mechanism by writing your own authentication handler class. This custom handler must extend org.apache.synapse.rest.AbstractHandler class and implement the handleRequest() and handleResponse() methods.

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