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

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.