Ran a question recently that was a bit tricky to solve with Azure API Management: How do you get a value passed in the URL Query String to your API operation from a policy in a <set-body> statement?

For example, let’s assume that the query string value we want is called userId. If you’re using a Liquid template, it would look something like this:

<set-body template="liquid">
    "userId": "{{context.Request.OriginalUrl.Query.userId}}"

Notice how we use OrigiinalUrl rather than Url. The former is the URL the consumer used to call into API Management, while the latter is the URL of the backend service.

If you’re not using a Liquid template, then you just need to make sure that your set-body expressoin explicitly returns a string object:

<set-body template="none">
    @("The user id is: " + context.Request.OriginalUrl.Query.GetValueOrDefault("userId"))

The set-body reference documentation provides some useful information on figuring stuff like this out, particularly when combined with the policy expressions documentation.

Tomas Restrepo

Software developer located in Colombia. Sr. PFE at Microsoft.