How to generate AWS S3 presigned URLs in .NET without third-party SDKs

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Developers building .NET applications often rely on the AWSSDK.S3 NuGet package to generate presigned S3 upload URLs, but this pulls in a large SDK that may be unnecessary for simple use cases. A lightweight alternative involves implementing the AWS Signature Version 4 signing process directly in code using built-in .NET cryptography libraries. The approach works with AWS S3 and compatible storage providers such as Cloudflare R2, Backblaze B2, DigitalOcean Spaces, and Hetzner Object Storage. The method generates a time-limited PUT URL with locked-in content type and file size constraints, requiring only the access key credentials to be stored as application secrets. This technique reduces external dependencies while still enabling secure, temporary file upload links for end users.

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Couple Builds AI Trip Planner Escapo to Simplify Travel Itinerary Planning

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Modal Labs Raises $355M Series C, Valued at $4.65B Amid AI Infrastructure Boom

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Munchable builds 450-word test suite to prevent silent gaps in food label scanning

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How Munchable built an allergen system that can only warn, never falsely clear

Munchable, an app helping people with IBS or reflux assess supermarket products, expanded in September 2024 to also flag declared allergens. Unlike its dietary condition logic, the allergen layer is designed to only add warnings and never mark a product as allergen-free, since absence of data is treated as silence rather than safety. This rule is enforced at three levels — in code logic, in result structure, and in a TypeScript type that contains no value for 'absent'. The system covers all 14 EU and UK regulated allergens, a superset of the US 'big nine', so warnings are not lost when users travel across regions. Careful distinctions are also made to avoid false positives, such as not treating an inferred generic 'nut' tag as evidence of peanuts unless that word appeared on the physical label.

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