policy.xml

<policies>
    <inbound>
        <base />

        <!-- Use a <choose> block to evaluate deployment-id -->
        <choose>
            <when condition="@(context.Request.MatchedParameters["deployment-id"] == "gpt-35-turbo-1106")">
                <set-backend-service backend-id="{backend-id-1}" />
            </when>
            <when condition="@(context.Request.MatchedParameters["deployment-id"] == "gpt-35-turbo-0125")">
                <set-backend-service backend-id="{backend-id-2}" />
            </when>
            <when condition="@(context.Request.MatchedParameters["deployment-id"] == "gpt-4o-2024-05-13")">
                <set-backend-service backend-id="{backend-id-3}" />
            </when>
            <otherwise>
                <set-backend-service backend-id="{backend-id-1}" />
            </otherwise>
        </choose>

        <authentication-managed-identity resource="https://cognitiveservices.azure.com" output-token-variable-name="managed-id-access-token" ignore-error="false" />

        <set-header name="Authorization" exists-action="override">
            <value>@("Bearer " + (string)context.Variables["managed-id-access-token"])</value>
        </set-header>
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>