Implement policies for APIs

In Azure, policies for APIs play a crucial role in managing and securing access to your resources. By implementing policies, you can define rules and constraints that govern the behavior of your APIs, ensuring compliance with organizational standards and best practices. In this article, we will explore how to implement policies for APIs when developing solutions for Microsoft Azure.

What are API Policies?

API policies act as a bridge between the API consumer and the API implementation. They enable you to modify, control, and monitor the traffic flowing through your API management solution. Policies allow you to add custom logic, enforce security measures, transform requests and responses, throttle traffic, and much more. Azure API Management provides a robust policy engine that offers a wide range of built-in policies and allows you to create custom policies to meet your specific requirements.

Enforcing HTTPS with a Policy

Securing API endpoints is essential to protect sensitive data and prevent unauthorized access. One of the most common policies used in Azure API Management is the requires-https policy, which enforces that all requests to an API must be made over HTTPS. To apply this policy, follow these steps:

1. Open the Azure portal and navigate to your API Management instance.
2. Go to the API you want to secure and select the “API” tab.
3. In the left-hand menu, click on “Policies” to open the policy editor.
4. Add the following policy to the inbound section:

xml

Save the policy and test the API by making a request. It should only accept HTTPS connections.

Implementing Rate Limiting Policies

Rate limiting helps prevent abuse and ensures fair usage of your APIs. Azure API Management provides rate limiting policies that allow you to restrict the number of calls a client can make within a specific time frame. To add rate limiting policies, use the following steps:

1. Open the Azure portal, go to your API Management instance, and select the desired API.
2. Click on the “Policies” tab and open the policy editor.
3. Add the following policies to the inbound section:

xml

The above policy limits the number of calls per key to 10 per 60-second window.

Transforming Request and Response with Policies

Azure API Management allows you to transform the request and response payloads using policies. This is handy in scenarios where you need to modify or enrich the data exchanged with your API. Here’s an example of transforming XML to JSON:

1. Open the Azure portal, navigate to your API Management instance, and select the desired API.
2. Open the policy editor by selecting the “Policies” tab.
3. Add the following policies to the inbound section:

xml




application/json


@{
var xmlData = context.Request.Body.As(preserveContent: true);
var jsonObject = JsonConvert.SerializeXmlNode(new XmlDocument().LoadXml(xmlData), Newtonsoft.Json.Formatting.None, true);
return jsonObject.ToString();
}

The above policy rewrites the incoming request URI, sets the backend service URL, changes the content type, and converts the XML request body to JSON before forwarding it to the backend.

Conclusion

Implementing policies for APIs in Azure provides powerful capabilities to manage and secure your APIs. By enforcing HTTPS, applying rate limiting, and transforming requests and responses, you can enhance the functionality, security, and performance of your APIs. Azure API Management’s policy engine offers a rich set of built-in policies and the ability to create custom policies, allowing you to tailor the behavior of your APIs to suit your specific requirements.