policy.xml

<policies>
    <inbound>
        <base />
        <authentication-managed-identity resource="https://cognitiveservices.azure.com" output-token-variable-name="managed-id-access-token" client-id="{{managed-identity-clientid}}" 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}" />
        <set-variable name="requestBody" value="@(context.Request.Body.As<string>(preserveContent: true))" />
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
        <choose>
            <when condition="@(context.Response.StatusCode == 200)">
                <log-to-eventhub logger-id="{eventhub-logger-name}">@{
                    var requestBody = (string)context.Variables["requestBody"];
                    var responseBody = context.Response.Body?.As<JObject>(preserveContent: true);
                    return new JObject(
                        new JProperty("id", responseBody?["id"]?.ToString() ?? Guid.NewGuid().ToString()),
                        new JProperty("timestamp", DateTime.UtcNow.ToString()),
                        new JProperty("model", responseBody?["model"]?.ToString() ?? "NA"),
                        new JProperty("modelRegion", context.Response.Headers.GetValueOrDefault("x-ms-region", "N/A")),
                        new JProperty("apimRequestId", context.Response.Headers.GetValueOrDefault("apim-request-id", "N/A")),
                        new JProperty("clientIp", context.Request?.IpAddress ?? "NA"),
                        new JProperty("operationName", context.Operation?.Name ?? "NA"),
                        new JProperty("request", requestBody),
                        new JProperty("response", responseBody?["choices"]?.ToString() ?? "N/A"),
                        new JProperty("promptTokens", responseBody?["usage"]?["prompt_tokens"]?.ToString() ?? "0"),
                        new JProperty("responseTokens", responseBody?["usage"]?["completion_tokens"]?.ToString() ?? "0"),
                        new JProperty("totalTokens", responseBody?["usage"]?["total_tokens"]?.ToString() ?? "0")
                        ).ToString();
                    }</log-to-eventhub>
            </when>
        </choose>
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>