Self-Issued OpenID Connect Provider (SIOP)

A Self-Issued OpenID Connect Provider (SIOP) is a profile of the OpenID Connect protocol where the user acts as their own OpenID Provider (OP). Instead of an external service like Google issuing the ID token, the user cryptographically signs a Verifiable Presentation or a Decentralized Identifier (DID)-based ID token directly from their own device or wallet. This enables passwordless authentication and user-centric data control.

SIOP enables blockchain-native login flows for dApps and services. A user can sign in by:

• Presenting a DID (e.g., did:ethr:...) from their wallet.
• Signing a SIOP request with their private key to create a verifiable credential.
• The relying party (RP) verifies the signature against the user's public key, enabling authentication without centralized servers, passwords, or OAuth providers.

The SIOP flow involves three main actors:

• Relying Party (RP): The application requesting authentication.
• SIOP (The User): The user acting as their own OpenID Provider.
• Verifiable Data Registry (e.g., a blockchain): Where the user's public key and DID are anchored.

The core artifact is the SIOP ID Token, a JSON Web Token (JWT) signed by the user's private key, containing claims like the DID and authentication context.

SIOP is a bridge between traditional federated identity (OIDC) and the decentralized identity stack. It is foundational for:

• W3C Decentralized Identifiers (DIDs): The user's identifier in the SIOP token.
• W3C Verifiable Credentials (VCs): SIOP tokens can be embedded within or presented alongside VCs.
• DID Auth protocols, which SIOP v2 and the emerging OpenID for Verifiable Credentials (OID4VC) specifications formalize.

SIOP is being adopted within the SSI (Self-Sovereign Identity) and enterprise blockchain ecosystems. Key implementations and frameworks include:

• Microsoft Entra Verified ID (uses SIOP-like flows for decentralized identity).
• Sphereon's SIOPv2 libraries for developers.
• European Digital Identity (EUDI) Wallet architecture, which incorporates SIOP principles for citizen authentication.

SIOP provides distinct advantages for user privacy and system resilience:

• No Central Provider: Eliminates dependency on platforms like Google or Facebook.
• Reduced Tracking: No single identity provider can track logins across all sites.
• Interoperability: Built on open standards (OIDC, JWT, DIDs).
• User Control: The user cryptographically proves ownership of their identifier without revealing their private key.

A primary risk is a malicious actor creating a fake Relying Party (RP) to trick a user's SIOP wallet into signing a Verifiable Presentation for the wrong audience or context. Mitigation relies on strong RP metadata verification and user education to scrutinize authorization requests.

• Example: A fake dApp could mimic a legitimate one, requesting a user's Decentralized Identifier (DID) and credentials for a harmful purpose.

Security hinges entirely on the user's ability to securely generate, store, and use their cryptographic keys. Loss of the private key means permanent loss of the DID and associated credentials. Solutions include:

• Hardware Security Modules (HSMs) or secure enclaves.
• Distributed Key Management systems to avoid single points of failure.
• User-friendly recovery mechanisms (e.g., social recovery, sharding) that don't compromise sovereignty.

SIOP responses (ID Tokens) must be protected against interception and reuse. Critical defenses include:

• Nonce and State Parameters: The RP provides a unique nonce in the request, which must be included and validated in the signed response.
• Audience (aud) Claim: The token must explicitly specify the RP's DID to prevent use elsewhere.
• Short Token Lifetimes: Limiting the validity of the signed response reduces the attack window.

Ensuring that a Verifiable Credential presented by a SIOP is genuinely bound to the presenter's DID is crucial. Threats include:

• Credential Theft: Stealing a credential and presenting it from a different DID.
• Mimicry: Using a similar-looking DID to impersonate the legitimate holder.

Defenses involve cryptographic proof-of-possession and verifying the credential's credentialSubject.id matches the presenter's DID.

The Decentralized Identifier (DID) itself can become a persistent correlator across different RPs if used indiscriminately. Privacy-preserving techniques are essential:

• Pairwise Pseudonymous DIDs: Generating a unique DID for each relationship to prevent cross-service tracking.
• Selective Disclosure: Using BBS+ signatures or zero-knowledge proofs to reveal only specific attributes from a credential, not the entire document.

The SIOP wallet (e.g., mobile app, browser extension) is a critical attack vector. Vulnerabilities can compromise all user identities. Key considerations:

• Secure Execution Environment: Protection against OS-level malware and side-channel attacks.
• User Consent UI: Clear, unambiguous interfaces that prevent users from accidentally signing malicious payloads.
• Regular Audits: Third-party security audits of the wallet's cryptographic libraries and network communication.

The website, application, or service that requests and verifies authentication or credentials from a user. In the SIOP flow, the RP is the verifier.

• Role: Initiates the SIOP/OIDC flow by sending an authentication request.
• Verification: Validates the ID Token and any Verifiable Presentations returned by the user's wallet.
• Example: A decentralized finance (DeFi) platform requiring proof of citizenship (a VC) for compliance.

A SIOP is implemented as a feature within a digital identity wallet or agent. These software components manage the user's DIDs, private keys, and Verifiable Credentials.

• Key Responsibilities:
  • Generate and store DIDs.
  • Securely sign JWTs for authentication.
  • Create Verifiable Presentations from stored credentials.
  • Interact with RP and Issuer endpoints.
• Examples: Trinsic, Spruce ID's didkit, Microsoft Entra Verified ID, and various open-source Aries Cloud Agent frameworks provide SIOP capabilities.

SIOP enables privacy-preserving, user-centric authentication across web and mobile applications.

• Decentralized Finance (DeFi): KYC/AML compliance without exposing full identity to every dApp.
• Enterprise Login: Passwordless, phishing-resistant access to corporate systems using employee-issued credentials.
• Government Services: Accessing digital services by presenting a verifiable government ID (e.g., driver's license).
• Social Media & Gaming: Portable, user-owned profiles and achievements that are not locked to a single platform.