Setting Up a Blockchain-Based Single Sign-On for Healthcare Networks

In healthcare, Single Sign-On (SSO) is essential for clinicians who need rapid access to multiple applications like Electronic Health Records (EHRs), lab systems, and pharmacy databases. Traditional SSO relies on a central identity provider (IdP) that acts as the sole gatekeeper for authentication. This centralization creates a single point of failure. A breach of the IdP—through credential theft, insider threats, or system vulnerabilities—can compromise access to every connected application across the entire healthcare network, exposing vast amounts of protected health information (PHI).

Beyond security, centralized SSO struggles with interoperability across disparate healthcare organizations. A physician consulting at multiple hospitals may need separate credentials for each network's SSO system, leading to password fatigue and insecure workarounds. Furthermore, patient data sharing for referrals or continuity of care often requires cumbersome, manual processes outside the SSO framework, violating principles of data minimization and patient consent. The current model is not designed for the decentralized, patient-centric future of healthcare.

A blockchain-based SSO system addresses these flaws by decentralizing control. Instead of a central database of credentials, verifiable credentials (VCs) and decentralized identifiers (DIDs) are issued and stored by the user. Authentication becomes a cryptographic proof presented by the user's digital wallet, verified against the blockchain's immutable ledger. This shift eliminates the central honeypot of data and gives patients and providers sovereign control over their identity and access permissions, enabling seamless yet secure cross-organizational workflows.

The foundation of a healthcare SSO system requires a robust technical stack. You will need a blockchain development environment such as Hardhat or Foundry for Ethereum-based solutions, or the Aptos CLI/Sui CLI for Move-based chains. A smart contract language like Solidity 0.8.x or Move is essential for writing the core identity logic. For the frontend, a framework like React or Next.js with a Web3 library such as Wagmi or ethers.js v6 is recommended. Finally, you must have access to a testnet (e.g., Sepolia, Amoy) for deployment and testing without using real funds.

The system architecture revolves around a decentralized identifier (DID) standard, typically W3C's DID specification. Each user or healthcare entity (like a hospital or clinic) controls a unique DID stored on-chain. The core smart contract acts as a verifiable data registry, mapping DIDs to public keys and service endpoints. Off-chain, a verifiable credential (VC) issuer (e.g., a medical board) signs attestations about a user's professional license. The user's wallet holds these VCs and can present verifiable presentations (VPs) to any participating healthcare dApp to prove their identity and permissions without revealing underlying data.

Key architectural decisions include choosing a blockchain layer. A private, permissioned chain like Hyperledger Fabric offers control and privacy for a consortium, while a public Layer 2 like Polygon zkEVM provides neutrality and cryptographic security with lower costs. You must also design the credential flow: the issuer signs a VC (e.g., {"credentialSubject": {"id": "did:ethr:0x...," "medicalLicense": "active"}}), which the user stores. When logging into a radiology portal, the portal requests a VP containing proof of an active license. The user's wallet signs a response with their private key, which the portal verifies against the on-chain DID document.

Security and privacy are paramount. The architecture must implement zero-knowledge proofs (ZKPs) using libraries like Circom or SnarkJS to allow users to prove credential attributes (e.g., "I am over 18" or "I am a licensed practitioner") without exposing the credential itself. Access control logic within the smart contract must enforce role-based permissions, ensuring only authorized issuers can write to a DID's record. Furthermore, all PII should be kept off-chain, with only cryptographic hashes (like keccak256) of consent receipts or audit logs stored on the blockchain for immutability.

Integration with existing healthcare systems requires building standardized APIs. The system should expose REST or GraphQL endpoints that translate traditional OAuth2/OIDC requests from an EHR system like Epic or Cerner into VC/VP requests. A relayer service may be necessary to pay blockchain gas fees on behalf of users for a seamless experience. Finally, plan for key management: will users use EOA wallets (seed phrase responsibility) or more user-friendly smart contract wallets (ERC-4337) with social recovery? This decision significantly impacts onboarding and long-term usability for non-technical medical staff.

Healthcare networks face significant challenges with interoperability and data silos. A blockchain-based Single Sign-On (SSO) system using Decentralized Identifiers (DIDs) and Verifiable Credentials (VCs) offers a solution. Unlike traditional SSO that relies on a central identity provider (like Google or Microsoft), a DID-based approach gives users self-sovereign control over their identity. This is critical for healthcare, where patient data privacy and portability between providers, insurers, and labs are paramount. The core components are the DID (a globally unique identifier), the DID Document (containing public keys and service endpoints), and VCs (tamper-proof digital claims).

The authentication flow, DID Auth, replaces passwords with cryptographic proofs. When a patient accesses a hospital portal, the site requests authentication. The patient's digital wallet (holding their private keys) creates a cryptographic signature linked to their DID. The hospital verifies this signature against the public key in the patient's DID Document, which is fetched from a verifiable data registry like a blockchain. This process establishes a secure session without the hospital ever storing a password. It enables passwordless, phishing-resistant login while giving the patient a unified identity across all participating healthcare entities.

For implementation, you must choose a DID method suitable for your blockchain. For Ethereum, did:ethr is common, while did:key is useful for testing. A patient's DID might look like did:ethr:0xabc123.... Their DID Document, resolvable via a universal resolver, contains authentication public keys. To issue a Verifiable Credential, such as a proof of insurance, an insurer signs a JSON-LD or JWT payload with their private key. The patient stores this VC in their wallet. During SSO, they can present a Verifiable Presentation containing this VC, allowing the hospital to verify both the patient's identity and their insurance status in one step.

A basic code snippet for generating a DID and signing an authentication challenge with ethr-did and ethr-did-resolver libraries illustrates the process:

javascriptCopy
import { EthrDID } from 'ethr-did';
import { Resolver } from 'did-resolver';
import { getResolver } from 'ethr-did-resolver';

// 1. Create a DID for a patient
const provider = /* your Ethereum provider */;
const patientDID = new EthrDID({
  identifier: '0xPatientAddress',
  provider,
  chainNameOrId: 'mainnet'
});
console.log('Patient DID:', patientDID.did);

// 2. Sign an authentication challenge
const challenge = 'HospitalLoginSession123';
const jwt = await patientDID.signJWT({ challenge });

// 3. Verifier resolves and checks the JWT
const resolver = new Resolver(getResolver());
const verificationResponse = await resolver.resolve(patientDID.did);
// Verify JWT signature against public key in DID Document...

Key architectural considerations include privacy-preserving data exchange. While DIDs are public, sensitive health data should never be stored on-chain. VCs contain only the necessary claims (e.g., "over 18") and use zero-knowledge proofs where possible. The system must integrate with existing Health Level Seven (HL7) FHIR standards for clinical data. Furthermore, key management is critical; loss of a private key means loss of identity. Solutions involve social recovery mechanisms or hardware security modules (HSMs) for institutional providers. Governance models for credential issuers (medical boards, hospitals) must also be established to ensure trust.

Adopting this architecture moves healthcare from fragmented, provider-centric identities to a patient-centric model. It reduces administrative overhead, enhances security against data breaches, and enables new applications like portable medical records and automated insurance claims. The next step is to pilot the system with a consortium of trusted partners, define the trust framework for issuers, and develop wallet applications that are accessible to non-technical users. Resources like the W3C Decentralized Identifiers specification and the Verifiable Credentials Data Model provide the foundational standards for building interoperable healthcare SSO.

A Login Verifiable Credential (Login VC) is a cryptographically signed attestation issued by a trusted Identity Provider (IdP) to a user. In a healthcare SSO context, this credential asserts a user's identity and their right to access a network of applications. Unlike traditional session cookies or OAuth tokens, a Login VC is a self-contained, user-owned credential that can be presented to any service within the trust framework without the IdP being contacted during the login flow. This model shifts control to the user and reduces central points of failure.

The credential is built on the W3C Verifiable Credentials Data Model standard. Its core data structure includes the issuer (your healthcare organization's IdP), the subject (the user's Decentralized Identifier or DID), and the claim (e.g., "role": "physician"). This data is then signed using the issuer's private key, creating a JSON Web Token (JWT) or similar proof. The signature allows any relying party (like an EMR application) to cryptographically verify the credential's authenticity and integrity without querying a central database.

To issue a credential, your Identity Provider must first establish a Decentralized Identifier (DID) for itself and for each user. A DID is a globally unique identifier, often stored on a blockchain or other decentralized system, that is controlled by the holder of its associated cryptographic keys. For a user, this is typically a DID:key or DID:web identifier. The issuer uses its DID and private key to sign the credential, binding the user's DID to the attested claims. This creates a portable, verifiable link between identity and access rights.

Here is a simplified example of a JWT-formatted Login VC payload for a physician:

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{
  "iss": "did:web:your-hospital.com",
  "sub": "did:key:z6Mkf5rGM...",
  "vc": {
    "@context": ["https://www.w3.org/2018/credentials/v1"],
    "type": ["VerifiableCredential", "LoginCredential"],
    "credentialSubject": {
      "id": "did:key:z6Mkf5rGM...",
      "role": "physician",
      "department": "cardiology",
      "npiNumber": "1234567890"
    }
  }
}

This payload is then signed to produce the final verifiable credential.

The issuance process is typically triggered after successful primary authentication (like an AD/LDAP or biometric login). The backend system generates the VC and delivers it to the user's digital wallet—a secure app on their device. The wallet holds the user's private keys and manages their credentials. By storing the Login VC locally, the user gains the ability to present it for SSO across participating healthcare applications, initiating a holder-initiated credential presentation flow for subsequent logins.

Key technical considerations for issuance include credential lifespan (short-lived for security), selective disclosure (to minimize data exposure), and revocation status. While the VC itself is self-contained, many systems use a revocation list (like a W3C Status List) or a smart contract on a blockchain to allow issuers to invalidate credentials if a user's access rights change or are revoked, ensuring the system remains secure and compliant with healthcare regulations.

The core of the SSO system is the patient's self-custodied wallet, which acts as a Verifiable Data Registry and a Holder in the W3C Verifiable Credentials data model. We will use MetaMask as the reference wallet for its widespread adoption and robust SDK. The first step is to establish a secure connection between the healthcare provider's dApp and the patient's wallet using the EIP-1193 standard. This allows the dApp to request the patient's public address, which serves as their decentralized identifier (DID). A common pattern is to use a library like wagmi or ethers.js to handle this connection seamlessly.

Once connected, the system must request the specific credentials needed for access. Instead of asking for broad permissions, the dApp requests a Selective Disclosure Verifiable Credential. For example, to book an appointment, the dApp might request proof that the user is over 18 and is a patient of 'General Hospital,' without needing their full name or date of birth. The patient's wallet receives this request, prompts the user for consent, and then generates a cryptographic proof (like a ZK-SNARK or BBS+ signature) that attests to the required claims. This proof is derived from a broader credential issued earlier by a trusted entity, such as a hospital.

The generated proof is then packaged into a Verifiable Presentation and signed by the patient's wallet. This presentation is sent back to the healthcare provider's backend for verification. The backend, acting as the Verifier, performs several checks: it validates the cryptographic signature of the presentation, verifies the proof against the public verification key of the credential's issuer (the hospital), and checks for revocation status, potentially by querying a smart contract on-chain. This entire flow ensures patient sovereignty, as they control what information is shared and with whom, moving beyond traditional, all-or-nothing data access models.

For developers, a critical implementation detail is managing session keys. After successful verification, the backend can issue a short-lived, traditional JWT session token to the patient's frontend application. This token grants access to the provider's internal APIs for the duration of a session. The key innovation is that this JWT is issued only after the decentralized, user-consented credential verification, linking the legacy authentication system to the new SSO layer. This hybrid approach allows for incremental adoption within existing healthcare IT infrastructure.

Security considerations are paramount. The wallet integration must guard against phishing and replay attacks. Always use eth_requestAccounts for initial connection and personal_sign for specific, domain-bound signature requests to prevent malicious sites from impersonating your dApp. Furthermore, the credential verification logic on-chain should include nonce checks and timestamp validation. Open-source libraries like Veramo or Spruce ID's Kepler can significantly reduce development risk by providing tested frameworks for managing DIDs, credentials, and presentations.

The Hospital Authentication Server (HAS) is the central authority in your SSO architecture. Its primary functions are to authenticate internal users via existing systems like Active Directory, mint W3C Verifiable Credentials (VCs) upon successful login, and manage the Decentralized Identifier (DID) for your hospital. We recommend using the SpruceID did:key method for its simplicity and the SpruceID credential-issuer library for VC creation. First, install the necessary packages: npm install @spruceid/didkit @spruceid/credential-issuer.

The server must generate and securely store a cryptographic key pair that forms the basis of the hospital's DID. This key is used to sign all issued credentials, providing cryptographic proof of their origin. Store the private key in a hardware security module (HSM) or a cloud-based key management service like AWS KMS or GCP Secret Manager. Never commit it to version control. The public key, along with the did:key method identifier, forms your hospital's DID document, which will be referenced by the blockchain resolver.

Upon a successful authentication event (e.g., a doctor logs into the internal portal), the HAS constructs a Verifiable Credential. A standard credential includes the doctor's DID (their blockchain identity), the hospital's DID as the issuer, a credentialSubject with attested claims (e.g., "role": "physician", "department": "cardiology"), and an expiration timestamp. The server then signs this credential JSON object with the hospital's private key using the EdDSA (Ed25519) algorithm, producing a JSON Web Signature (JWS).

Finally, the HAS needs to expose two critical endpoints. A POST /issue-credential endpoint that receives authentication proofs from your internal system and returns the signed VC. And a public GET /.well-known/did.json endpoint that serves the hospital's DID document. This document must include the public key in JWK format and the assertionMethod verification relationship, allowing any verifier (like another hospital's gateway) to cryptographically verify the signatures on your issued credentials.

In a traditional SSO system, session management relies on a central server maintaining a session cookie or token. In a decentralized model, the session state is anchored to the user's Decentralized Identifier (DID) and a Verifiable Presentation (VP). When a user authenticates, the healthcare application receives a signed VP containing their verified credentials (e.g., medical license, practitioner role). The application's backend validates this VP's signature against the issuer's DID on the blockchain and caches the user's permissions for a configurable period, establishing a local session without centralized state.

The session's security depends on the integrity of the VP and the user's control of their private keys. A common pattern is to issue a short-lived OAuth 2.0 access token or a signed JWT to the frontend client after successful VP validation. This token, which references the DID and VP hash, is used for API calls. The backend validates this token's signature and checks the associated permissions. This hybrid approach leverages familiar web security patterns while the underlying authority remains decentralized.

Secure logout in this context has two critical components: client-side token invalidation and optional on-chain revocation signaling. The immediate step is for the client application to discard its access token and session data. For enhanced security, especially if a device is lost or compromised, the user can revoke the specific Verifiable Credential presented during login. This is done by publishing a revocation status list entry, such as a Bitstring Status List, to the blockchain, linking it to the credential's unique identifier.

Applications must check credential status upon each sensitive transaction or at regular intervals. For example, before allowing access to patient records, the backend can resolve the credential's status from the chain. Libraries like veramo or did-jwt-vc provide methods for this verification. This ensures that a logged-out or revoked session cannot be resurrected, even if the old access token is somehow retained.

Implementing this requires careful event listening and state synchronization. Your application backend should listen for CredentialRevoked events from your smart contract or monitor the relevant status list registry. When a revocation is detected, any active local sessions associated with that credential must be terminated immediately. This creates a robust system where user-controlled revocation on the blockchain propagates to all relying applications.

This guide demonstrated a practical architecture using Ethereum for identity anchoring, Ceramic for portable data streams, and Lit Protocol for encrypted, condition-based access. The core components you've implemented—a DID for each entity, a Verifiable Credential for professional licensure, and a token-gated API—create a system where access is cryptographically verifiable and patient data remains encrypted until access conditions are met. This moves beyond simple authentication to provide a full attestation and authorization framework.

For production deployment, several critical next steps are required. First, implement a robust key management strategy, likely using multi-party computation (MPC) or hardware security modules (HSMs) for institutional private keys. Second, integrate with existing hospital Identity Providers (IdPs) like Active Directory via SAML or OIDC bridges to ensure clinician adoption. Third, establish a clear legal and operational framework for credential issuance and revocation, defining trusted issuers (e.g., state medical boards) and procedures for handling disputes.

To extend the system's capabilities, consider implementing more granular attribute-based access control (ABAC) using projects like Oasis Protocol or Hyperledger Fabric Private Data Collections. Explore zero-knowledge proofs (ZKPs) via zkSNARKs (using libraries like Circom and snarkjs) to allow verification of credential predicates (e.g., "is a licensed cardiologist") without revealing the underlying credential data. This significantly enhances privacy for complex, multi-party healthcare workflows.

The final, crucial phase is auditing and compliance. Regularly audit all smart contracts with firms like Trail of Bits or OpenZeppelin. Ensure the system aligns with regulations like HIPAA for data privacy and GDPR for right to erasure, potentially by storing only pointers and hashes on-chain. Continuous monitoring of access logs and anomaly detection is essential for maintaining trust and security in a live healthcare environment.