Add [FunctionUrl] annotation attribute with CORS support and source generator

What is this?

Adds first-class support for Lambda Function URLs to the Lambda Annotations framework. Function URLs give your Lambda function a dedicated HTTPS endpoint without needing API Gateway — ideal for webhooks, simple APIs, and microservices.

Usage

[LambdaFunction]
[FunctionUrl(AuthType = FunctionUrlAuthType.NONE)]
public IHttpResult GetItems([FromQuery] string category, ILambdaContext context)
{
    return HttpResults.Ok(new { items = new[] { "item1", "item2" }, category });
}

This generates a handler that accepts HTTP API v2 payloads and emits a FunctionUrlConfig in your SAM template — no API Gateway resource needed.

CORS support

[FunctionUrl(AuthType = FunctionUrlAuthType.NONE,
             AllowOrigins = new[] { "https://example.com" },
             AllowMethods = new[] { "GET", "POST" },
             AllowHeaders = new[] { "Content-Type" },
             AllowCredentials = true,
             MaxAge = 3600)]

CORS configuration is optional — the Cors block is only emitted when at least one CORS property is set.

Authentication

Two auth modes via FunctionUrlAuthType:

• NONE — Public endpoint, anyone with the URL can invoke the function
• AWS_IAM — Only authenticated IAM users/roles can invoke the function

Key points

• Function URLs only support the HTTP API v2 payload format (APIGatewayHttpApiV2ProxyRequest/Response), so the source generator always uses v2 types — there is no version selection like [HttpApi] has
• All existing parameter binding ([FromQuery], [FromHeader], [FromBody], [FromRoute]) and IHttpResult returns work out of the box
• Generates FunctionUrlConfig as a property on the function resource (not as an event source), matching the SAM specification
• Automatically cleans up FunctionUrlConfig from the template when the attribute is removed
• Handles switching between [FunctionUrl] and [HttpApi]/[RestApi] seamlessly
• Detects [FunctionUrl] without [LambdaFunction] and reports a diagnostic error

Related: DOTNET-8569