What is digital signing? (beginner here)

General
1

Hi everyone!

I’m pretty new to digital signing and trying to understand how it works in API integrations.

I’m already familiar with API keys and have a basic understanding of OAuth 2.0 Bearer tokens (still learning!), but once digital signatures entered the picture, I honestly started feeling a bit overwhelmed.

A few things I’m hoping to better understand:

  • What does “digitally signing a request” actually mean in simple terms?

  • I’ve seen terms like JWS and FAPI mentioned, are these standards we’re expected to follow?

  • From an implementation standpoint, what does the process typically look like?

  • Any common beginner mistakes I should watch out for?

If anyone can share a beginner-friendly explanation, learning resources, or even practical tips from experience, I’d really appreciate it.

Thanks in advance!

2

In simple terms, digital signing proves that you sent the request and that it hasn’t been altered in transit.

A simple way to think about it:

  • OAuth token = “I’m authorized to access this API.”
  • Digital signature = “This exact message came from me and hasn’t been tampered with.”

How digital signing works

When digitally signing a request, the client typically:

  1. Takes selected parts of the HTTP request (e.g., method, URL, headers, body).
  2. Creates a cryptographic hash of that data (commonly SHA-256).
  3. Signs that hash using its private key.
  4. Sends the generated signature along with the request.

On the server side:

  1. The server retrieves the sender’s public key.
  2. Recomputes the hash from the received request.
  3. Verifies the signature using the public key.

If verification succeeds:

  • The request is authentic (came from the expected sender).
  • The request integrity is intact (not modified).

If it fails:

  • The message may have been altered.
  • Or the signature was generated incorrectly.

JWS and FAPI

  • JSON Web Signature (JWS) - A standard format for representing digital signatures using JSON. It defines how to structure and encode the header, payload, and signature.
  • Financial-grade API (FAPI) – A security profile for high-risk ecosystems (e.g., financial services). It defines stricter requirements around OAuth, cryptographic algorithms, and request signing.

A Few Notes:

  • Digital signing does not require JWS.
  • FAPI is not a signing mechanism — it is a security rulebook that may require JWS-based signing.
  • Digital signatures can exist independently of both.

I’m also continuing to learn about this topic, so if anyone here has hands-on implementation experience and can share practical insights or lessons learned, that would be greatly appreciated. :slight_smile: