How to get proxy not to error when context attribute is not present?

Question

I am using the below snippet in inbound

<set-header name="caller-data" exists-action="override">

<value>@(context.User.Email)</value>

<value>@(context.User.FirstName)</value>

<value>@(context.User.LastName)</value>

</set-header>

Works great when there is a user associated with the subscription. However on sub keys which doesn't have a user associated the proxy errors and returns status 500 (internal error). Is there a way to tell the context evaluation to return null value rather than an error in situations where the context attribute is not available?

Answer 1

In Azure API Management (APIM), you can use policy expressions to handle cases where context attributes may not be available. The policy expressions are written in C# and allow for conditional logic. This way, you can set a default value (like an empty string) if the user attributes are not available, preventing the API from returning a 500 error.

Here’s how you can modify your <set-header> policy to handle cases where context.User attributes may not be available:

<set-header name="caller-data" exists-action="override">

    <value>@(!String.IsNullOrEmpty(context?.User?.Email) ? context.User.Email : "null")</value>

    <value>@(!String.IsNullOrEmpty(context?.User?.FirstName) ? context.User.FirstName : "null")</value>

    <value>@(!String.IsNullOrEmpty(context?.User?.LastName) ? context.User.LastName : "null")</value>

</set-header>

In this snippet:

• The ?. operator is a null-conditional operator that ensures that if context.User is null, the expression will short-circuit and return null without throwing an error.
• The ? : operator is a ternary conditional operator that checks if the value is not null or empty and returns it; otherwise, it returns "null".

Example with Default Values

If you prefer to set default values rather than "null":

<set-header name="caller-data" exists-action="override">

    <value>@(!String.IsNullOrEmpty(context?.User?.Email) ? context.User.Email : "default-email@example.com")</value>

    <value>@(!String.IsNullOrEmpty(context?.User?.FirstName) ? context.User.FirstName : "DefaultFirstName")</value>

    <value>@(!String.IsNullOrEmpty(context?.User?.LastName) ? context.User.LastName : "DefaultLastName")</value>

</set-header>

Detailed Breakdown:

1. Check if context.User.Email is not null or empty:
   • !String.IsNullOrEmpty(context?.User?.Email) ? context.User.Email : "null"
   • If context.User.Email is available, use it; otherwise, use "null".
2. Check if context.User.FirstName is not null or empty:
   • !String.IsNullOrEmpty(context?.User?.FirstName) ? context.User.FirstName : "null"
   • If context.User.FirstName is available, use it; otherwise, use "null".
3. Check if context.User.LastName is not null or empty:
   • !String.IsNullOrEmpty(context?.User?.LastName) ? context.User.LastName : "null"
   • If context.User.LastName is available, use it; otherwise, use "null".

By incorporating these checks, you ensure that your API does not return a 500 error when the context attributes are not available and instead gracefully handles the absence of user data.