C#

Handle Viewer webhooks in C#.

This page is the C# implementation guide: verify signatures, then handle only the events you enabled.

Webhook security

All webhook requests from Avara are signed using HMAC-SHA256 with Standard Webhooks headers (webhook-id, webhook-timestamp, webhook-signature). Copy the webhook secret from API Config (View Webhook Secret) and set it as the AVARA_WEBHOOK_KEY environment variable. The SDK’s unwrap() method reads that variable, verifies the signature, and returns a typed event. Every Avara→partner POST expects HTTP 200 with a JSON body matching that event’s response schema. Synchronous hooks should respond within about 30 seconds.

using Microsoft.AspNetCore.Mvc;
using Avara;
using Avara.Models.Webhooks;

[ApiController]
[Route("webhooks")]
public class WebhookController : ControllerBase
{
    private readonly AvaraClient _client = new(); // reads AVARA_WEBHOOK_KEY from env

    [HttpPost("avara")]
    public async Task<IActionResult> HandleWebhook()
    {
        using var reader = new StreamReader(Request.Body);
        var body = await reader.ReadToEndAsync();
        var webhookEvent = _client.Webhooks.Unwrap(body, GetHeaders());

        switch (webhookEvent)
        {
            case StudyAccessRequestedWebhookEvent e:
            {
                // Handle study access request
                var studyId = e.Data.StudyId;
                break;
            }

            case SecondaryCaptureAccessRequestedWebhookEvent e:
            {
                // Handle secondary capture upload request
                var studyId = e.Data.StudyId;
                break;
            }

            case ModalityWorklistRequestedWebhookEvent e:
            {
                // Handle modality worklist request
                var clinicId = e.Data.ClinicId;
                break;
            }
        }

        return Ok();
    }

    private Dictionary<string, IEnumerable<string>> GetHeaders()
    {
        return Request.Headers.ToDictionary(
            h => h.Key,
            h => (IEnumerable<string>)h.Value.ToArray()
        );
    }
}

Study Image Access

The study.access_requested webhook is sent when Avara needs presigned URLs for DICOM images (and optional non-DICOM media). This is a synchronous (hard) webhook — you must respond within about 30 seconds. This webhook is sent before a study can be viewed in the Avara interface.

When Avara needs to access study images, it sends a POST request to your webhook endpoint. Your endpoint must respond with presigned GET URLs. The SDK’s unwrap() method returns a typed StudyAccessRequestedWebhookEvent that you can use directly.

Return authorized: false with an error when the caller must not access the study. Returning authorized: true with an empty urls array (and omitted or empty mediaUrls) is treated as no data available, not as a denial.

using Microsoft.AspNetCore.Mvc;
using Avara;
using Avara.Models.Webhooks;

[ApiController]
[Route("webhooks")]
public class WebhookController : ControllerBase
{
    private readonly AvaraClient _client = new();

    [HttpPost("avara")]
    public async Task<IActionResult> HandleWebhook()
    {
        using var reader = new StreamReader(Request.Body);
        var body = await reader.ReadToEndAsync();
        var webhookEvent = _client.Webhooks.Unwrap(body, GetHeaders());

        if (webhookEvent is StudyAccessRequestedWebhookEvent e)
        {
            var studyId = e.Data.StudyId;
            var studyInstanceUid = e.Data.StudyInstanceUid;

            // This is your internal business logic
            var presignedUrls = GeneratePresignedUrlsForStudy(studyInstanceUid);

            if (presignedUrls.Count == 0)
            {
                return Ok(new { authorized = false, error = "Study not found in PACS" });
            }

            return Ok(new { authorized = true, urls = presignedUrls });
        }

        return Ok();
    }

    // This is your internal business logic
    private List<string> GeneratePresignedUrlsForStudy(string studyInstanceUid)
    {
        // Query your PACS/RIS system for the study
        // Generate presigned URLs for each DICOM image
        // Return a flat list of all image URLs
        return new List<string>
        {
            "https://storage.example.com/dicom/image1.dcm?token=abc123",
            "https://storage.example.com/dicom/image2.dcm?token=def456",
        };
    }

    private Dictionary<string, IEnumerable<string>> GetHeaders()
    {
        return Request.Headers.ToDictionary(
            h => h.Key,
            h => (IEnumerable<string>)h.Value.ToArray()
        );
    }
}

Response Format

public class StudyAccessRequestedWebhookResponse
{
    public bool Authorized { get; set; }
    public List<string> Urls { get; set; } // Flat list of DICOM GET URLs (may be empty)
    public List<StudyAccessRequestedMediaUrl>? MediaUrls { get; set; }
    public string? Error { get; set; }
}

public class StudyAccessRequestedMediaUrl
{
    public string Url { get; set; }
    public string MimeType { get; set; }
    public string? FileName { get; set; }
}

Secondary Capture Upload

The secondary_capture.access_requested webhook is sent when a viewer user creates a secondary capture. This is a synchronous (hard) webhook — you must return presigned PUT URLs in-request, within about 30 seconds.

Avara asks for upload URLs before writing the generated DICOM to your storage. The SDK’s unwrap() method returns a typed SecondaryCaptureAccessRequestedWebhookEvent. Respond authorized: false with an error if the study cannot be written. uploadUrls must be PUT-capable; the client uploads with Content-Type: application/dicom and writes the same object to every URL. Series and SOP UIDs are provided when available so you can pre-compute object keys. If you send contentCreatorName, Avara ignores it and derives the creator name server-side.

using Microsoft.AspNetCore.Mvc;
using Avara;
using Avara.Models.Webhooks;

[ApiController]
[Route("webhooks")]
public class WebhookController : ControllerBase
{
    private readonly AvaraClient _client = new();

    [HttpPost("avara")]
    public async Task<IActionResult> HandleWebhook()
    {
        using var reader = new StreamReader(Request.Body);
        var body = await reader.ReadToEndAsync();
        var webhookEvent = _client.Webhooks.Unwrap(body, GetHeaders());

        if (webhookEvent is SecondaryCaptureAccessRequestedWebhookEvent e)
        {
            var studyId = e.Data.StudyId;
            var studyInstanceUid = e.Data.StudyInstanceUid;
            var seriesInstanceUid = e.Data.SeriesInstanceUid;
            var sopInstanceUid = e.Data.SopInstanceUid;

            // This is your internal business logic
            var uploadUrls = GenerateSecondaryCaptureUploadUrls(
                studyInstanceUid,
                seriesInstanceUid,
                sopInstanceUid
            );

            if (uploadUrls.Count == 0)
            {
                return Ok(new { authorized = false, error = "Study cannot be written" });
            }

            return Ok(new { authorized = true, uploadUrls });
        }

        return Ok();
    }

    // This is your internal business logic
    private List<string> GenerateSecondaryCaptureUploadUrls(
        string studyInstanceUid,
        string? seriesInstanceUid,
        string? sopInstanceUid
    )
    {
        // Generate presigned PUT URLs for the secondary capture DICOM
        return new List<string>
        {
            "https://storage.example.com/dicom/sc/image.dcm?token=abc123",
        };
    }

    private Dictionary<string, IEnumerable<string>> GetHeaders()
    {
        return Request.Headers.ToDictionary(
            h => h.Key,
            h => (IEnumerable<string>)h.Value.ToArray()
        );
    }
}

Response Format

public class SecondaryCaptureAccessRequestedWebhookResponse
{
    public bool Authorized { get; set; }
    public List<string> UploadUrls { get; set; }
    public string? ContentCreatorName { get; set; } // Ignored if provided
    public string? Error { get; set; }
}

Modality Worklist

The modality_worklist.requested webhook is sent when an on-prem modality (via an Avara PACS box) issues a C-FIND MWL. This is a synchronous (hard) webhook — the C-FIND path waits on your response, which should return within about 30 seconds.

Avara forwards the query window to your endpoint. Only one active API key per organization may have the Modality Worklist Webhook Endpoint set. The SDK’s unwrap() method returns a typed ModalityWorklistRequestedWebhookEvent. Return authorized: false with an error to surface a worklist failure to the modality. items is required and may be empty when there are no scheduled exams.

Item field names are PascalCase DICOM-style (not camelCase). StudyInstanceUID is required from the partner RIS today — do not omit it. PatientName, PatientID, and Modality must be non-empty. ScheduledProcedureStepSequence must contain at least one step.

using Microsoft.AspNetCore.Mvc;
using Avara;
using Avara.Models.Webhooks;

[ApiController]
[Route("webhooks")]
public class WebhookController : ControllerBase
{
    private readonly AvaraClient _client = new();

    [HttpPost("avara")]
    public async Task<IActionResult> HandleWebhook()
    {
        using var reader = new StreamReader(Request.Body);
        var body = await reader.ReadToEndAsync();
        var webhookEvent = _client.Webhooks.Unwrap(body, GetHeaders());

        if (webhookEvent is ModalityWorklistRequestedWebhookEvent e)
        {
            var clinicId = e.Data.ClinicId;
            var callingAe = e.Data.CallingAe;
            var sourceIp = e.Data.SourceIp;
            var dateStart = e.Data.DateStart;
            var dateEnd = e.Data.DateEnd;
            var modality = e.Data.Modality;

            // This is your internal business logic
            var items = QueryModalityWorklist(
                clinicId, callingAe, sourceIp, dateStart, dateEnd, modality
            );

            return Ok(new Dictionary<string, object>
            {
                ["authorized"] = true,
                ["items"] = items,
            });
        }

        return Ok();
    }

    // This is your internal business logic
    private List<Dictionary<string, object>> QueryModalityWorklist(
        string clinicId,
        string callingAe,
        string sourceIp,
        string dateStart,
        string dateEnd,
        string? modality
    )
    {
        var step = new Dictionary<string, object>
        {
            ["ScheduledProcedureStepStartDate"] = "20260813",
            ["ScheduledProcedureStepStartTime"] = "090000",
            ["ScheduledProcedureStepID"] = "SPSID-1",
            ["Modality"] = "CT",
            ["ScheduledProcedureStepDescription"] = "CT CHEST WO CONTRAST",
        };

        var item = new Dictionary<string, object>
        {
            ["PatientName"] = "DOE^JANE",
            ["PatientID"] = "MRN12345",
            ["PatientBirthDate"] = "19800115",
            ["PatientSex"] = "F",
            ["PatientSize"] = "1.65",
            ["PatientWeight"] = "62",
            ["Modality"] = "CT",
            ["AccessionNumber"] = "ACC-1001",
            ["StudyInstanceUID"] = "1.2.840.113619.2.55.3.604688119.868.1234567890.123",
            ["RequestedProcedureDescription"] = "CT CHEST WO CONTRAST",
            ["StudyDescription"] = "CT CHEST WO CONTRAST",
            ["ProtocolName"] = "CHEST_WO",
            ["ScheduledProcedureStepSequence"] = new List<Dictionary<string, object>> { step },
        };

        return new List<Dictionary<string, object>> { item };
    }

    private Dictionary<string, IEnumerable<string>> GetHeaders()
    {
        return Request.Headers.ToDictionary(
            h => h.Key,
            h => (IEnumerable<string>)h.Value.ToArray()
        );
    }
}

Response Format

public class ModalityWorklistRequestedWebhookResponse
{
    public bool Authorized { get; set; }
    public List<ModalityWorklistItem> Items { get; set; }
    public string? Error { get; set; }
}

public class ModalityWorklistItem
{
    public string PatientName { get; set; }
    public string PatientID { get; set; }
    public string PatientBirthDate { get; set; }
    public string PatientSex { get; set; }
    public string PatientSize { get; set; }
    public string PatientWeight { get; set; }
    public string Modality { get; set; }
    public string AccessionNumber { get; set; }
    public string StudyInstanceUID { get; set; }
    public string RequestedProcedureDescription { get; set; }
    public string StudyDescription { get; set; }
    public string ProtocolName { get; set; }
    public List<ModalityWorklistScheduledStep> ScheduledProcedureStepSequence { get; set; }
}

public class ModalityWorklistScheduledStep
{
    public string ScheduledProcedureStepStartDate { get; set; }
    public string ScheduledProcedureStepStartTime { get; set; }
    public string ScheduledProcedureStepID { get; set; }
    public string Modality { get; set; }
    public string ScheduledProcedureStepDescription { get; set; }
}