eventgrid-apim-policy.xml

<policies>
    <inbound>
        <base />
        <!-- Check event type -->
        <set-variable value="@(context.Request.Headers["Aeg-Event-Type"].Contains("SubscriptionValidation"))" name="isEventGridSubscriptionValidation" />
        <set-variable value="@(context.Request.Headers["Aeg-Event-Type"].Contains("Notification"))" name="isEventGridNotification" />
        <choose>
            <when condition="@(context.Variables.GetValueOrDefault<bool>("isEventGridSubscriptionValidation"))">
                <return-response>
                    <set-status code="200" reason="OK" />
                    <set-body>@{
                          var events = context.Request.Body.As<string>(); 
                          JArray a = JArray.Parse(events);
                          var eventGridData = a.First["data"];
                          var validationCode = eventGridData["validationCode"];
                          var jOutput =
                             new JObject(
                                new JProperty("validationResponse", validationCode)
                             );
                        return jOutput.ToString();
                    }</set-body>
                </return-response>
            </when>
            <when condition="@(context.Variables.GetValueOrDefault<bool>("isEventGridNotification"))">
                <send-one-way-request mode="new">
                    <set-url>https://hooks.slack.com/services/{{slack-key}}</set-url>
                    <set-method>POST</set-method>
                    <set-body>@{  
                        var events = context.Request.Body.As<string>(); 
                        JArray a = JArray.Parse(events);
                        var eventGridData = a.First["data"];
                        var station = eventGridData["station"];
                        var artist = eventGridData["artist"];
                        var song = eventGridData["song"];
                        return new JObject(  
                            new JProperty("username", station),  
                            new JProperty("icon_emoji", ":musical_note:"),  
                            new JProperty("text", String.Format("Just added: {0}, {1}",
                                song, artist))
                            ).ToString();   
                    }</set-body>
                </send-one-way-request>
                <return-response>
                    <set-status code="200" reason="OK" />
                </return-response>    
            </when>
        </choose>
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>