A developer’s guide to eSign APIs

eSignatures are the new normal for businesses. The digital world has made it easier and faster for businesses to sign agreements and approve transactions. Asking clients to come into the office to sign documents is a thing of the past.

So what’s the next step up from basic eSignature tools? To fully benefit from eSignatures, you need an eSign API that’s compatible with your platform.

But what does this involve, and how difficult is is to build?

Why buy an eSign API?

Yes, you could build it yourself. You know this means months of hard work and huge resource investment. What you might not know is the difficulty in building an eSignature API isn’t just on the development side; it’s a legal issue.

eSignature legality is subject to a vast range of regional and international laws and regulations. You need to ensure your eSignatures are legally binding in your market of operation – if this is a single US state, meeting these requirements might be straightforward. If it’s international, you have a whole basket of regulations to consider.

Meeting legal requirements can take as long as the development work itself. Purchasing an API that already meets these can save plenty of time – and money, in the long run.

How to secure eSignatures 

If you need signing then you need security. The documents your customers are working with are mostly at risk from user error, but you should ensure they're protected against bad actors as well as possible.

When you integrate with an API, check it’s compatible with the security measures you already have in place. These might be data encryption, access controls and third-party testing.

Key technical insights

For developers, one major benefit of a plug-in API is the world of possibilities. Because you’re not having to do the bulk of the work of creating an eSignature workflow within your product, you have more time to focus on your ideal outcome; not your minimal viable product.

A few key technical elements it’s good to be across include:

Authentication

Many eSignature APIs rely on OAuth 2.0 for authentication. Developers need to set up OAuth flows, including managing client credentials, authorization codes and handling refresh tokens securely.

Additionally, some eSignature APIs use keys for access. It’s crucial to secure these keys, following best practices like environment variable storage and avoiding hardcoding in your source code.

Data security and compliance

eSign APIs often implement encryption for documents and signatures, both at rest and in transit. Developers should ensure encryption is enabled and understand how it protects sensitive data.

This encryption is a necessary part of APIs meeting compliances: you should ensure any API you choose is compliant with regulations in your area of operation - this could be eIDAS, the ESIGN Act, UETA or several others.

Error handling and rate limiting

APIs return standard error codes like 400 (bad request), 401 (unauthorized), and 429 (too many requests). Developers should implement error handling to manage these effectively and improve user experience.

APIs can also impose rate limits to prevent abuse. Developers should handle rate limits gracefully, using retry mechanisms and exponential backoff strategies to avoid disruptions in service.

Make integration easy

Many eSignature APIs offer SDKs and libraries for languages like Python and JavaScript, simplifying integration. Leverage these tools to speed up development and reduce errors.

Testing and sandbox best practices

You’ll need to perform test runs prior to implementing an eSign API. The easiest way to do this is inside a sandbox: a safe space to test out the API without affecting production data. Playing around in a sandbox is often free.

The testing phase can uncover problems likely to arise in the integration process. To get the most out of your testing, here are some scenarios you can run:

• simulating user flows – check that creating, sending, signing and receiving documents runs smoothly
• signing timing - what happens when multiple people hop in and sign at the same time? Or when the primary signer is unavailable and passes the document on, or just straight up declines?
• bulk signing - what’s the largest number of signers or documents this API can cope with?
• testing edge cases – how is the workflow affected if connection drops? When the file is too large? When a signer quits mid-signing?