Azure API management: Set different backend url for different endpoints

Question

I have an Azure API which have multiple endpoints and it calls different backend service with different api-keys.
Eg:

1. /offer endpoint in azure apim calls : https://offerBackend/offers
2. /offer/{id} - https://offerBackend/offers/{id}
3. /products - https://productBackend/products
4. /customer - https://customerBackend/customer

I am trying to use set-backend-service based on the endpoint being called, like:

<policies>
    <inbound>
        <base />
        <!-- Start:Set Different backends on basis of endpoints -->
            <when condition="@(context.Request.Url.Path.Contains("offer"))">
                <set-backend-service base-url="https://offerBackend" />
            </when>
            <when condition="@(context.Request.Url.Path.Contains("product"))">
                <set-backend-service base-url="https://productBackend" />
            </when>
            <when condition="@(context.Request.Url.Path.Contains("customer"))">
                <set-backend-service base-url="https://customerBackend" />
            </when>
        <!-- End:Set Different backends on basis of endpoints -->
    </inbound>

But for these different backends I need to pass different credentials i.e. api-key in header.How can I do that?

Answer 1

The when elements do not have the parent element choose.
Example:

<choose>
    <when condition="Boolean expression | Boolean constant">
        <!— one or more policy statements to be applied if the above condition is true  -->
    </when>
    <when condition="Boolean expression | Boolean constant">
        <!— one or more policy statements to be applied if the above condition is true  -->
    </when>
    <otherwise>
        <!— one or more policy statements to be applied if none of the above conditions are true  -->
    </otherwise>
</choose>

---

You can specify the api-keys as named values to store them as secrets:

The named value can be used as header value for authentication to the backend:

<set-header name="api-key" exists-action="override">
   <value>{{offer-api-key}}</value>
</set-header>
<set-backend-service base-url="https://offerBackend" />

The complete policy:

<policies>
    <inbound>
        <base />
        <!-- Start:Set Different backends on basis of endpoints -->
        <choose>
            <when condition="@(context.Request.Url.Path.Contains("offer"))">
                <set-header name="api-key" exists-action="override">
                    <value>{{offer-api-key}}</value>
                </set-header>
                <set-backend-service base-url="https://offerBackend" />
            </when>
            <when condition="@(context.Request.Url.Path.Contains("product"))">
                <set-header name="api-key" exists-action="override">
                    <value>{{product-api-key}}</value>
                </set-header>
                <set-backend-service base-url="https://productBackend" />
            </when>
            <when condition="@(context.Request.Url.Path.Contains("customer"))">
                <set-header name="api-key" exists-action="override">
                    <value>{{customer-api-key}}</value>
                </set-header>
                <set-backend-service base-url="https://customerBackend" />
            </when>
        </choose>
        <!-- End:Set Different backends on basis of endpoints -->
    </inbound>

A different solution is, to use backends and configure URL, authentication, ... in one place:

This can be used in the set-backend-service policy

<when condition="@(context.Request.Url.Path.Contains("offer"))">
      <set-backend-service backend-id="Offer" />
</when>

The complete inbound policy with Backend-Ids:

<policies>
    <inbound>
        <base />
        <!-- Start:Set Different backends on basis of endpoints -->
        <choose>
            <when condition="@(context.Request.Url.Path.Contains("offer"))">
                <set-backend-service backend-id="Offer" />
            </when>
            <when condition="@(context.Request.Url.Path.Contains("product"))">
                <set-backend-service backend-id="Product" />
            </when>
            <when condition="@(context.Request.Url.Path.Contains("customer"))">
                <set-backend-service backend-id="Customer" />
            </when>
        </choose>
        <!-- End:Set Different backends on basis of endpoints -->
    </inbound>