Below is the link to reference/examples of using Azure API management policy

• https://github.com/Azure/api-management-policy-snippets/tree/master/examples

There’s an example there on how to Mask Asynchronous calls as Synchronous API however for my requirement it’s not enough.

The target API behaves as follow:

1. All operations are POST and asynchronous.
2. To get the results of any operation a second API needs to be called and it’s expecting the transaction id.
3. API expects a payload in command manner (args parameter) instead of proper JSON name/value pair.

Requirement: API should return the results in synchronous manner.

Solution:

API Callout Policy in API Management.

Steps: 

1. Create a GET operation and via policy rewrite the operation to POST
2. Create a JSON transformation logic in the inbound policy and execute the backend API.
3. Create a JSON transformation logic in outbound policy and add a retry policy to execute the second API  that returns the result passing the transaction id from #2
4. Return the results from second API.

Policy Code:

application/json




@{
var paramFromRequest = Uri.UnescapeDataString(context.Request.OriginalUrl.Query.GetValueOrDefault("paramFromRequest"));
JObject transBody = new JObject();
transBody.Add("source", 
     new JObject
     {
         {"someproperty", "fixvalue"},
         {"someproperty2", "fixvalue2"},
     });

//Add all json properties as arg
transBody.Add("args", JToken.FromObject(new[] 
{ 
      paramFromRequest
}));
return transBody.ToString();
}
@(context.Request.Body.As(true))


POST












@{ 
var url = context.Api.ServiceUrl+ "{{SECONDBACKENDAPI_URL}}";
return url;
}
POST

@(context.Variables.GetValueOrDefault("authorization"))


application/json

@(context.Variables.GetValueOrDefault("jsonPayload"))

())" />


@((context.Variables.GetValueOrDefault("results")["{{PROPERTYNAME IN JSON OBJECT THAT CONTAINS THE RESULT}}"].ToString()))