Complete Guide to Azure API Management Policy

Azure API Management Policy is a powerful tool that helps you manage and secure APIs. It provides a centralized platform for API developers to create, publish, and manage APIs, while also offering advanced security features to protect against threats.

APIs can be exposed to various security risks, such as unauthorized access and data breaches. Azure API Management Policy helps mitigate these risks by providing features like authentication, authorization, and rate limiting.

To get started with Azure API Management Policy, you need to create a policy that defines the rules and behaviors for your APIs. This policy can be applied at various levels, including at the API level, product level, or subscription level.

Configuration is key to making Azure API Management Policy work for you. You can configure policy definitions using simple XML documents that describe a sequence of statements to apply to requests and responses.

The portal provides a guided, form-based editor to simplify configuring popular policies without coding XML, as well as a code editor where you can insert XML snippets or edit XML directly. This makes it easy to get started and experiment with different configurations.

The policy XML configuration is divided into inbound, backend, outbound, and on-error sections, which are executed in order for a request and a response.

To configure Azure APIM, you'll need to have an API configured, like the sample conferenceapi. You can then configure the OPA URL and any required token via Named values.

The external authorizer policy can be added to Azure APIM at the global, product, API, or operation level. For inbound evaluation, you can capture the request and pass it to OPA via an HTTP call.

If a denied response is received from OPA, an HTTP 403 Forbidden status code is returned. If the OPA call is not successful, the status code and reason are returned instead. Otherwise, Azure APIM will continue its execution and call the configured backend.

Here's a summary of the configuration options:

Error handling is a crucial aspect of Azure API Management policy. If an error occurs during request processing, the system skips any remaining steps in the inbound, backend, or outbound sections and jumps to the on-error section.

The on-error section allows you to review the error using the context.LastError property. You can also inspect and customize the error response using the set-body policy.

By placing policy statements in the on-error section, you can configure what happens if an error occurs. This is particularly useful for setting up error handling mechanisms that work best for your specific API.

Here are some key things to keep in mind when working with error handling in Azure API Management policy:

You can use Microsoft Copilot in Azure to create policies for Azure API Management, which provides policy authoring capabilities. This allows you to create policies without knowing the syntax.

To get started, prompt Copilot in Azure to generate policy definitions, then copy the results into the policy editor and make any necessary adjustments. You can ask questions to gain insights into different options, modify the provided policy, or clarify the policy you already have.

APIM policy documents can also be written using GitHub Copilot, which suggests possible completions as you type. This can be especially helpful when applying a CORS policy between frontend and backend applications at the global level.

Transformation is a powerful tool in API Management policies. It allows you to modify the incoming request or outgoing response to suit your needs.

You can change the HTTP method for a request using the Set request method policy. This is useful when you need to convert a request from one method to another.

The Set status code policy is another useful tool for transformation. It allows you to change the HTTP status code to a specified value.

You can also use the Set variable policy to persist a value in a named context variable for later access. This is useful when you need to store a value temporarily for use in later policies.

The Set body policy sets the message body for a request or response. This is useful when you need to modify the content of a request or response.

The Set HTTP header policy assigns a value to an existing response and/or request header or adds a new response and/or request header. This is useful when you need to add or modify headers in a request or response.

The Set query string parameter policy adds, replaces the value of, or deletes a request query string parameter. This is useful when you need to modify the query string parameters in a request.

The Rewrite URL policy converts a request URL from its public form to the form expected by the web service. This is useful when you need to modify the URL of a request.

Here is a summary of the transformation policies available in API Management:

Microsoft Copilot in Azure provides policy authoring capabilities for Azure API Management, allowing you to create policies without knowing the syntax.

You can use Copilot in Azure in the context of API Management's policy editor to generate policy definitions, which you can then copy into the policy editor and make any necessary adjustments.

To get started with Copilot in Azure, you can prompt it to generate policy definitions, then copy the results into the policy editor and make any necessary adjustments.

Copilot in Azure can also help you gain insights into different options, modify the provided policy, or clarify the policy you already have.

Policy expressions can be used to modify requests, such as adding user data to the incoming request with the set-header policy.

In the example, a policy expression is used to add a header with the user ID associated with the subscription key in the request and the region where the gateway processing the request is hosted.

You can write APIM policy documents at the global, API, and operation levels, and the context is slightly different.

To write a global policy document, you can use a zero-shot prompt in GitHub Copilot, which will suggest something you might want, and you can then modify the policy document as needed.

You can also use GitHub Copilot to write operation-level policy documents, such as adding a CORS policy to the global policy document.

GraphQL resolver policies are a crucial part of API Management. They're configured using policies scoped to a specific operation type and field in a GraphQL schema.

You can specify a GraphQL resolver to use HTTP API, Cosmos DB, or Azure SQL data sources. For example, you can configure a single http-data-source policy with elements to specify a request to an HTTP data source.

You can't include a resolver policy in policy definitions at other scopes, such as API, product, or all APIs. This means it doesn't inherit policies configured at other scopes.

The gateway evaluates a resolver-scoped policy after any configured inbound and backend policies in the policy execution pipeline.

Here are some key things to keep in mind about GraphQL resolver policies:

Authentication and authorization are crucial steps in securing your API. You can enforce the existence and/or value of an HTTP header with policies like Check HTTP header, which is available in both Classic and V2 policies.

The Check HTTP header policy is a great way to ensure that a specific header is present in every request. This policy is available in all policy types, including Consumption, Self-hosted, and Workspace policies.

You can also get the authorization context of a specified connection to a credential provider with the Get authorization context policy. This policy is available in both Classic and V2 policies.

If you need to restrict calls from specific IP addresses and/or address ranges, you can use the Restrict caller IPs policy. This policy is available in all policy types, including Consumption, Self-hosted, and Workspace policies.

Here are some of the authentication and authorization policies available:

These policies can be used to enforce various authentication and authorization scenarios, and they are all available in different policy types.