Electronic signature URL authentication is now a control point

At a glance

What this is: This is an analysis of why public electronic signature URLs need signer authentication to prevent unauthorized access to agreements and associated personal data.

Why it matters: It matters because IAM, NHI, and lifecycle teams all have to treat document access as an identity problem, not just a workflow problem, when links can be forwarded, intercepted, or scanned.

👉 Read OneSpan's analysis of how to secure electronic signature URLs

Context

An eSignature URL is effectively a bearer link if it is not bound to a verified signer. In practice, that means anyone who obtains the link can reach the signing ceremony, which turns document delivery into an access-control problem rather than a simple communications problem.

For IAM and identity governance teams, the issue is not limited to human authentication. It sits at the intersection of account opening, contract approval, customer onboarding, and delegated access, where the proof of identity must exist before the document becomes reachable.

Key questions

Q: How should security teams protect electronic signature URLs from unauthorized access?

A: They should require signer authentication before the document opens, not after the link is delivered. The practical control is to bind the signing ceremony to a verified identity, then choose the weakest authentication method that still satisfies the legal, fraud, and audit requirements for that transaction.

Q: Why do public eSignature links create identity and data risk?

A: Because a public link behaves like a bearer credential. If someone gets the URL, they may reach the signing flow without proving who they are, which can expose contracts, personal data, and account-opening materials to misuse, forwarding, or automated harvesting.

Q: What do organisations get wrong about eSignature authentication?

A: They often treat authentication as an optional user-experience setting instead of a core access control. That mistake leads to inconsistent assurance levels, weak evidentiary value, and a signing process that cannot reliably prove the identity of the person who accepted the agreement.

Q: How do teams choose between OTP, KBA, certificates, and passkeys for signing?

A: They should choose based on transaction risk, dispute likelihood, and compliance needs. Low-risk workflows may tolerate simpler methods, but regulated or high-value documents need stronger proof of identity and better audit evidence, especially when the signature could later be challenged.

Technical breakdown

Public signing URLs and bearer-access risk

A public eSignature URL behaves like a reusable access token unless the workflow adds an identity check. When the link is sent by email or SMS, it may pass through infrastructure that can inspect message content, which means the URL can be observed outside the intended recipient path. Without signer authentication, the system relies on possession of the link alone, which is not enough to prove identity. The control boundary is therefore the signing ceremony itself, not the notification channel.

Practical implication: bind each signing link to a verified identity step before document access is granted.

Signer authentication methods and assurance levels

Signer authentication is not one control but a set of assurance patterns. Security questions, KBA, SMS OTP, certificate-based authentication, government digital credentials, hardware tokens, and FIDO passkeys each create different levels of confidence in the signer's identity. The right choice depends on transaction risk, user friction, and the legal need to prove who signed. Lower-assurance methods may be acceptable for routine requests, but they create weaker evidence when a signature must stand up to dispute or audit.

Practical implication: match authentication strength to document risk, evidentiary need, and regulatory exposure.

Embedded workflows versus exposed links

An embedded signing flow changes the threat model because the user authenticates to the host application first, and the signing transaction is reached inside that authenticated session. A public link model does the opposite, placing the document behind a URL that can be distributed directly and later consumed by whoever possesses it. That distinction matters because the exposed-link model is far more dependent on the signer verification step. In governance terms, the workflow design determines whether identity is established at entry or deferred until after exposure.

Practical implication: prefer embedded or pre-authenticated signing journeys where business risk justifies tighter control.

Threat narrative

Attacker objective: The attacker wants to obtain sensitive agreement data and identity information, then use it to support fraud, impersonation, or broader account abuse.

1. Entry occurs when an exposed signing URL is obtained from email, SMS, or another message path that does not itself verify the recipient.
2. Escalation occurs when the link is opened without signer authentication, allowing access to contracts, onboarding records, or other sensitive transaction data.
3. Impact occurs when the attacker retrieves personally identifiable information or uses the exposed documents for fraud, impersonation, or social engineering.

Breaches seen in the wild

• Schneider Electric credentials breach — exposed credentials gave attackers access to Schneider Electric Jira, exfiltrating 40GB.
• DeepSeek breach — DeepSeek breach exposed 1M+ log lines and sensitive secret keys.

Read our 52 NHI Breaches Analysis report for a comprehensive view of breaches impacting Non-Human Identities including AI Agents.

NHI Mgmt Group analysis

Signer authentication is the control that turns a signature URL from a bearer link into an identity-bound transaction. Without that binding, the workflow assumes possession of a link is enough to authorise access, which is not a defensible identity premise. That is not a minor configuration issue, it is a governance failure because the system cannot distinguish the intended signer from anyone who intercepts the URL. Practitioners should treat signing URLs as identity-bearing access paths, not notifications.

Public eSignature links create trust debt because the workflow externalises identity proof until after exposure has already occurred. The document exists in a reachable state before the signer has been verified, which means the organisation is accepting a period of uncontrolled access as normal operating design. That pattern is especially weak for account opening, mortgage, insurance, and other high-value transactions where the documents themselves carry enough information to support later fraud. Practitioners should regard exposed-link signing as a data-governance risk, not only an authentication choice.

Authentication strength must be aligned to the legal and operational value of the transaction, not to user convenience alone. KBA, OTP, certificate-based authentication, smart cards, and FIDO passkeys all produce different evidence quality, and the weakest acceptable option is often the one most likely to be overused. Identity governance fails when a single signing pattern is applied across every transaction regardless of risk. Practitioners should establish assurance tiers for signing workflows and map them to document sensitivity, dispute potential, and regulatory requirements.

eSignature governance now overlaps with broader identity lifecycle controls because access to a document can be the first step in account creation, credential issuance, or contractual authority. That makes signer verification part of the joiner and onboarding story, not just a transaction-security detail. When the signature is the trigger for downstream access, the control must be reviewed with the same discipline as any other identity proofing and authorisation checkpoint. Practitioners should place signing workflows inside the same governance model used for high-risk identity events.

AI-assisted scanning raises the stakes because exposed signing URLs can be found and weaponised at scale. The article's threat model is no longer limited to accidental forwarding or human discovery; it now includes machine-driven harvesting of live links from message paths and shared surfaces. That shifts the problem from isolated link protection to systematic exposure management. Practitioners should assume eSignature URLs are discoverable assets and govern them accordingly.

From our research:

• The average estimated time to remediate a leaked secret is 27 days, despite 75% of organisations expressing strong confidence in their secrets management capabilities, according to The State of Secrets in AppSec.
• Only 44% of developers are reported to follow security best practices for secrets management, exposing a significant developer behaviour gap, according to The State of Secrets in AppSec.
• For the broader governance angle, review The 52 NHI breaches Report for patterns in exposed credentials and downstream access abuse.

What this signals

Bearer-link governance is the real issue here: when a signing URL can be opened before identity is verified, the organisation is effectively outsourcing access control to the network path and the message channel. That pattern belongs in the same risk conversation as exposed credentials and unmanaged tokens, especially when transactions can trigger account creation or contractual authority.

The next programme decision is whether your eSignature workflow is designed for convenience first or evidentiary integrity first. In practice, that means defining which document classes require stronger proofing, where embedded authentication is justified, and how much exposure you will accept before identity is checked.

The governance signal is clear: once AI can scan exposed URLs at scale, link protection stops being a messaging concern and becomes an access-management problem. Teams that already manage secrets, certificates, and workload identity should extend the same discipline to signing links and transaction URLs.

For practitioners

• Bind every public signing URL to signer verification Require authentication before the document ceremony opens, rather than relying on the link itself as proof of entitlement. For higher-risk transactions, step up from basic OTP to stronger factors such as certificate-based authentication or FIDO passkeys.
• Segment signing workflows by transaction risk Create assurance tiers for routine, regulated, and high-value agreements so the authentication method matches the legal and fraud impact of the document. Keep the policy simple enough that business teams can apply it consistently without guessing.
• Treat eSignature links as sensitive access paths Limit how signing URLs move through email, SMS, and support channels, and assume message infrastructure may inspect the link. Review notification design with the same scrutiny you would apply to any other bearer credential.
• Review embedded signing for high-exposure use cases Where user friction and business risk allow, move from exposed public links to authenticated embedded journeys so identity is established earlier in the flow. That reduces the chance that a raw URL becomes the only gate to a sensitive agreement.

Key takeaways

• Public eSignature URLs are access paths, not harmless notifications, when they are not bound to signer authentication.
• The security and legal value of a signature depends on the assurance level used to prove the signer before document access is granted.
• Organisations should classify signing workflows by risk and move high-exposure transactions to stronger authentication and earlier identity proofing.

Key terms

• eSignature URL: A signing link that directs a user to an electronic document ceremony. When the link is not tied to a verified identity, it behaves like a bearer path and can be opened by anyone who obtains it, regardless of the intended recipient.
• Signer Authentication: The identity check used before a person can access or complete an electronic signature transaction. It can range from simple one-time codes to certificates, passkeys, or government credentials, depending on the evidence required and the risk of the document.
• Evidentiary Integrity: The degree to which a signing workflow can prove who signed, when they signed, and under what controls. Strong evidentiary integrity matters when agreements are disputed, regulated, or used to trigger downstream access or financial commitments.
• Bearer Link: A link that grants access to whoever holds it, rather than to a specifically verified identity. In identity governance terms, bearer links create exposure because possession alone becomes the access criterion, which is rarely sufficient for sensitive transactions.

Deepen your knowledge

NHI governance, agentic AI identity, and machine identity lifecycle are core topics in our NHI Foundation Level course, the industry's only accredited NHI security programme. If you are responsible for identity security strategy or NHI governance in your organisation, it is worth exploring.

This post draws on content published by OneSpan: Comment protéger vos adresses URL de signature électronique contre les cyberattaques. Read the original.