policy.xml

<policies>
    <inbound>
        <base />
        <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>
        <set-backend-service backend-id="{backend-id}" />
        <!-- Reused the following policy: https://github.com/Azure/enterprise-azureai/blob/main/infra/modules/apim/policies/api_policy_openai.xml -->
        <choose>
            <when condition="@(context.Request.Body.As<JObject>(true)["stream"] != null && context.Request.Body.As<JObject>(true)["stream"].Type != JTokenType.Null)">
                <set-variable name="isStream" value="@{
                    var content = (context.Request.Body?.As<JObject>(true));
                    string streamValue = content["stream"].ToString();
                    return streamValue;
                }" />
            </when>
        </choose>
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
        <set-header name="x-ms-stream" exists-action="override">
            <value>@{
                    return context.Variables.GetValueOrDefault<string>("isStream","false").Equals("true", StringComparison.OrdinalIgnoreCase).ToString();
                }</value>
        </set-header>
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>