A policy template is an XML document that provides directives to change the behavior of an API request or response. This mechanism is immensely useful in a variety of scenarios involving Microsoft Power Automate or Microsoft Power Apps, for example, when you want to add default parameter values or modify HTTP headers.
The policy template you define is tied to an operation of a custom connector. This operation could be anything that triggers a specific action in the app, such as creating a record, updating a record, or deleting a record. Therefore, you are able to customize the behavior for different operations, helping you to meet various business requirements.
Implementing Policy Templates
To incorporate a policy template, you need to navigate to the definition tab of the custom connector in Power Apps or Power Automate. Here you can modify the request and response using the policy template. The policy template is divided into two sections: inbound and backend.
Inbound refers to the policies that apply when a request is received, prior to being processed by the backend service. On the other hand, backend refers to the policies applied after processing the request by the backend service, before the response is returned to the client.
Examples of Policy Templates
Let’s delve into examples showcasing how to use policy templates to modify connector behavior at runtime in Power Platform.
Consider a use case where we need to add a specific header “X-Custom-Header: example” in all API requests from the connector.
The policy template would look like this:
In this scenario, the set-header directive is used to define the new header, and exists-action set to override ensures the header is updated even if it already exists in the request.
Another popular use-case is setting default query parameter. The template could look this way:
Once implemented, this policy ensures that the query parameter queryParam is always set to default in all requests.
Conclusion
Understanding and effectively applying policy templates is a critical aspect for PL-400 Microsoft Power Platform Developer exam aspirants. They allow you to modify the behavior of Power Apps or Power Automate connectors dynamically at runtime, providing additional flexibility to meet business needs. Furthermore, they cement a strong foundation for handling more complex scenarios and delivering more comprehensive developer objectives.
Practice Test
True or False: Policy templates in Microsoft Power Platform allow the modification of connector behavior at runtime.
- True
- False
Answer: True
Explanation: Policy templates provide a way to modify the behavior of a connector during its execution, adding more flexibility and control to your connector’s behavior at runtime.
Which of the following describes the function of a policy template in Microsoft Power Platform?
- A) It changes the connector behavior at compile-time.
- B) It allows documenting connector behavior.
- C) It modifies the connector behavior at runtime.
- D) It adapts the UI of the connector.
Answer: C
Explanation: Policy templates change the connector behavior at runtime, giving you more control on how the connector behaves during its execution.
What does the “ModifyRequest” policy template do in Power Platform?
- A) It changes the request content type.
- B) It adds a tracking ID to a response.
- C) It changes the response content type.
- D) It changes URI path of the request.
Answer: D
Explanation: The “ModifyRequest” policy template allows you to change the URI path of the request being processed.
True or False: Policy templates in Microsoft Power Platform can help in adding a security layer to your connectors.
- True
- False
Answer: True
Explanation: You can use a policy template to enforce a specific security model, such as OAuth, to your connectors at runtime, adding a layer of security to your connectors.
In Power Platform, where do you apply policy templates?
- A) On the connector’s UI elements
- B) During connector’s compile-time
- C) On the connector’s runtime behavior
- D) On the connector’s static properties
Answer: C
Explanation: Policy templates are designed to modify the runtime behavior of connectors in Power Platform.
True or False: Applying a policy template is a reversible process.
- True
- False
Answer: True
Explanation: You can remove or change an applied policy template thereby changing the behavior of the connector again.
Which of the following can be achieved by using a policy template?
- A) Add an additional tracking parameter in the request
- B) Modifying the URI path of the request
- C) Changing the response content
- D) All of the above
Answer: D
Explanation: These are among the usages of policy templates in Power Platform’s connectors at runtime.
True or False: You can create custom policy templates.
- True
- False
Answer: True
Explanation: Power Platform allows developers to create custom policy templates, meeting their specific needs.
Which of the following policy templates ensures that only HTTPS traffic is allowed?
- A) LimitCallRateByKey
- B) RequireHttps
- C) SetQueryParam
- D) SendRedirect
Answer: B
Explanation: The “RequireHttps” policy template enforces that all traffic is sent over HTTPS.
True or False: Policy templates cannot be used to modify response data in Power Platforms.
- True
- False
Answer: False
Explanation: Policy templates can be used to modify both request and response data in Power Platform connectors at runtime.
Interview Questions
What is the purpose of policy templates in modifying connector behavior at runtime?
Policy templates allow developers to insert a variety of policies into the processing pipeline of API Management, which can be used to change the behavior of the API by manipulation and transformation of the API input and output, and by enforcing specific control flows.
How can policy templates aid in customization in Microsoft Power Platform?
Policy templates in Microsoft Power Platform can aid in customization by letting developers modify connector behavior at runtime. This can involve changing the original behavior of requests and responses or influencing control flows such as caching and choosing which API version to use.
How are policy templates applied to connectors?
Policy templates are applied to connectors by including them within the inbound, backend, outbound, and on-error policy sections of the connector.
Where are policy templates defined in Microsoft Power Platform?
Policy templates are defined within the context of a policy scope, such as a Product, API, Operation, or All APIs.
What is the “inbound” section in the context of policy templates and connectors?
The “inbound” section pertains to requests entering the API Management gateway from a client application before they’re forwarded to the backend service. It’s where developers can define policies to process or customize incoming requests.
Can you alter the response from a backend service using policy templates?
Yes, you can use the “outbound” section in the policy template to alter the response from a backend service before it is sent back to the client application.
What actions can a “backend” section in policy templates perform?
The “backend” section in policy templates is used for controlling the forward request to and the response from the backend service. It can include actions like setting the backend service, URL rewrite, or load balancing.
What does the “on-error” section of a policy template do?
The “on-error” section in policy templates is used when an unhandled exception occurs during policy execution or backend request. It allows developers to handle exceptions or errors effectively.
Can you explain the purpose of the “base” policy in API Management?
The “base” policy in API Management provides a predefined set of rules and behaviors that are applied to all the APIs within the scope. It serves as the default policy when there are no specific policies defined.
Is it possible to insert custom code in policy templates?
Yes, policy templates allow the insertion of custom code, such as C# functions, which can be used at runtime to perform custom processing and manipulation.
How is the order of policy execution determined in Microsoft Power Platform?
The order of policy execution in Microsoft Power Platform is determined primarily by the location of the policy in the hierarchical policy scope: from outermost (all APIs) to innermost (operation).
Can policies be applied conditionally in Microsoft Power Platform?
Yes, policies in Microsoft Power Platform can be applied conditionally by using the “choose” policy statement which allows to include “when” clauses to apply policies according to certain conditions.
What role do variables play in connector policies?
Variables in connector policies help by storing and restating values within or across policies. They can control flow logic, store the results of policy statements for later use, or to modify the behavior of other policy statements.
Can you name some types of policy templates available in Microsoft Power Platform?
Key types of policy templates in Microsoft Power Platform include control flow, conversion, set variable, caching, set HTTP header, find and replace, restrict caller IPs, and validate JWT among others.
What are context variables in the context of policy execution?
Context variables are built-in variables that provide information about the current state of policy execution, including details about the request, response, operation, and API. They are read-only and cannot be modified.
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