Add E-Signatures to .NET (C#)

Quick start

1. Get an API key from signb.ee (free, no credit card)
2. Set SIGNBEE_API_KEY in your environment
3. Add the code below to your app

.NET (C#) example

[ApiController]
[Route("api/[controller]")]
public class ContractController : ControllerBase
{
    private readonly HttpClient _http;

    public ContractController(HttpClient http) => _http = http;

    [HttpPost("send")]
    public async Task<IActionResult> Send([FromBody] ContractRequest req)
    {
        _http.DefaultRequestHeaders.Authorization =
            new AuthenticationHeaderValue("Bearer",
                Environment.GetEnvironmentVariable("SIGNBEE_API_KEY"));

        var response = await _http.PostAsJsonAsync(
            "https://signb.ee/api/send", req);
        var result = await response.Content.ReadAsStringAsync();
        return Ok(result);
    }
}

What happens

1. Your app sends markdown or a PDF URL to Signbee
2. Signbee generates a PDF (if markdown) and emails the recipient a signing link
3. Recipient signs — both parties receive the signed PDF with SHA-256 certificate

Also works with AI agents

Install the MCP server to let Claude, Cursor, or Windsurf send documents directly:

npx -y signbee-mcp

Integration details

.NET is Microsoft's enterprise application framework used by millions of developers. Adding e-signatures uses HttpClient with dependency injection — the standard pattern for external API calls in .NET.

HttpClient management: Never create new HttpClient instances per request — this causes socket exhaustion. Use IHttpClientFactory (registered in Program.cs) for connection pooling and lifecycle management. The example shows constructor injection of HttpClient.

Named or typed clients: For production, register a named or typed HttpClient in Program.cs with pre-configured base address and headers. This centralises configuration and avoids repeating authorization headers in every controller.

Minimal API alternative: .NET 6+ supports Minimal APIs for lightweight endpoints. Replace the controller with a single app.MapPost() call for a more concise integration. Both approaches work identically with the Signbee API.

Configuration: Store SIGNBEE_API_KEY in appsettings.json, user-secrets (development), or Azure Key Vault (production). Use the IOptions pattern for type-safe configuration binding. Never hardcode API keys in source files.

Azure deployment: Signbee works seamlessly on Azure App Service, Azure Functions, and Azure Container Apps. Store the API key in Azure Key Vault and reference it in App Configuration for secure, centralised secrets management.

FAQs