Authentication Protocols Comparison

This document provides a comprehensive comparison of major authentication protocols, highlighting their key characteristics, use cases, strengths, and weaknesses.

Protocol Comparison Table

Aspect	OIDC (OpenID Connect)	SAML (Security Assertion Markup Language)	Kerberos	LDAP	OAuth 2.0
Primary Purpose	Authentication & basic user profile	Authentication & authorization	Authentication	Directory services & authentication	Authorization (delegated access)
Year Introduced	2014	2005 (SAML 2.0)	1980s	1993	2012
Format	JSON/JWT	XML	Binary tickets	LDAP entries	JSON
Protocol Base	Built on OAuth 2.0	SOAP and XML	Custom (Kerberos v5)	LDAP protocol	REST
Transport	HTTPS	Various bindings (HTTP, SOAP)	UDP/TCP	TCP/IP	HTTPS
Token/Artifact	ID Token (JWT)	SAML Assertion	Tickets (TGT, ST)	N/A (directory entries)	Access Token
Token Information	Claims about user identity	Assertions about user	Encrypted user/service info	Directory attributes	Resource access permissions
Token Lifespan	Typically short (minutes to hours)	Typically longer (hours to days)	Short (typically 8-10 hours)	N/A	Variable (minutes to days)
Single Sign-On	Yes	Yes	Yes	Partial (through integration)	No (but enables OIDC which does)
Federated Identity	Yes	Yes	Limited (cross-realm)	No (but can be a backend)	No (but enables OIDC which does)

Detailed Feature Comparison

Feature	OIDC	SAML	Kerberos	LDAP	OAuth 2.0
Mobile/SPA Friendly	★★★★★	★★	★	★★	★★★★★
Enterprise Adoption	★★★★	★★★★★	★★★★★	★★★★★	★★★★
Implementation Ease	★★★★	★★	★	★★	★★★★
Security Robustness	★★★★	★★★★	★★★★★	★★★	★★★
Standardization	★★★★★	★★★★★	★★★★	★★★★	★★★★★
Scalability	★★★★★	★★★★	★★★	★★★★	★★★★★
Cross-Domain Support	★★★★★	★★★★★	★★	★★★	★★★★★
Developer Popularity	★★★★★	★★★	★★	★★★	★★★★★

Protocol Use Cases

Protocol	Primary Use Cases	Less Suitable For
OIDC	• Modern web applications • Mobile applications • APIs • Consumer-facing services	• Legacy enterprise systems • Environments with extensive SAML investment
SAML	• Enterprise applications • B2B federation • Complex authorization scenarios • Legacy system integration	• Mobile applications • Modern SPAs • Consumer-facing services
Kerberos	• Windows domain authentication • Enterprise internal networks • Database authentication • On-premises services	• Internet-facing applications • Mobile applications • Cross-organizational auth
LDAP	• User directory services • Organizational hierarchies • Application authentication backend • Network device authentication	• Modern web authentication • Consumer-facing services • Mobile applications
OAuth 2.0	• API authorization • Delegated access • Third-party integration • Resource access control	• Direct user authentication • Enterprise single sign-on • Credential management

Technical Characteristics

Characteristic	OIDC	SAML	Kerberos	LDAP	OAuth 2.0
Authentication Mechanism	Various (via OAuth 2.0 flows)	Browser redirects, POST bindings	Ticket-based with shared secrets	Bind operation with credentials	Various (authorization code, implicit, etc.)
Message Exchange Pattern	Front-channel & back-channel	Primarily front-channel via browser	Direct client-server	Direct client-server	Front-channel & back-channel
Cryptography	JWT signing/encryption (RSA, ECDSA)	XML-DSig, XML-Enc	Symmetric (DES, AES) & Asymmetric	TLS, SASL (optional)	TLS, JWT (optional)
Identity Provider Discovery	Dynamic discovery via .well-known	Metadata XML files	Configured realms	Directory service queries	N/A
Session Management	Various methods (cookies, tokens)	IDP-initiated, SP-initiated logout	Ticket renewal, TGT	Application-specific	Token management
Claims/Attribute Format	JSON claims	XML attributes	PAC (Privilege Attribute Certificate)	LDAP attributes	JSON claims (scope-based)

Integration Complexity

Integration Aspect	OIDC	SAML	Kerberos	LDAP	OAuth 2.0
Server Implementation	Moderate	Complex	Very Complex	Moderate	Moderate
Client Implementation	Easy	Moderate	Complex	Easy	Easy
Configuration Complexity	Low to Moderate	Moderate to High	High	Moderate	Low to Moderate
Required Infrastructure	HTTPS	HTTPS	KDC, Sync Clocks	Directory Servers	HTTPS
Testing Difficulty	Moderate	Moderate to High	High	Moderate	Moderate
Debugging Ease	Good (readable JWT)	Moderate (XML parsing)	Difficult (binary)	Moderate	Good (readable tokens)

Security Considerations

Security Aspect	OIDC	SAML	Kerberos	LDAP	OAuth 2.0
Password Transmission	Never (proper implementation)	Never (proper implementation)	Never	Cleartext or protected	N/A (delegated)
Replay Protection	Yes (nonce, timestamps)	Yes (timestamps, IDs)	Yes (timestamps)	No (by default)	Yes (state parameter)
Key Management	PKI	PKI	Key Distribution Center	Application-specific	PKI
Common Vulnerabilities	Token leakage, CSRF	XML attacks, certificate issues	Clock skew, ticket theft	Injection, unencrypted comms	Token leakage, CSRF
MFA Support	Excellent	Good	Limited	Limited	Through extensions
Revocation Support	Limited (short token life)	Good	Good	Excellent	Limited

Database Integration (PostgreSQL)

Integration Aspect	OIDC	SAML	Kerberos	LDAP	OAuth 2.0
Native Support in PostgreSQL	No	No	Yes (GSSAPI)	Yes	No
Implementation Pattern	Application-level or proxy	Application-level or proxy	Direct connection	Direct connection	Application-level or proxy
Connection Security	Application manages	Application manages	Native ticket auth	Native binding	Application manages
Role Mapping	App maps claims to roles	App maps assertions to roles	Principal maps to user	DN maps to user	App maps scopes/claims to roles
Setup Complexity	Moderate	High	Moderate to High	Moderate	Moderate
Common Use Case	Web app accessing database	Enterprise app accessing database	Domain-joined systems	Directory-integrated systems	API accessing database

Real-World Implementation Notes

Protocol	Implementation Notes
OIDC	• Widely supported in modern libraries and frameworks • Good client support across languages • Growing adoption by major identity providers • Well-suited for cloud-native applications
SAML	• Mature enterprise tooling • Extensive vendor support • Well-documented security practices • Often requires specialized knowledge
Kerberos	• Built into Windows domains (Active Directory) • Requires careful network and time configuration • Strong for internal network authentication • Limited usability across organizational boundaries
LDAP	• Primarily a directory service with authentication capabilities • Often used as a backend for other auth systems • Provides rich attribute storage and querying • Requires proper security configuration
OAuth 2.0	• Primarily for authorization, not authentication • Powers many API authorization scenarios • Foundation for OIDC • Limited by itself for comprehensive identity scenarios

Conclusion

No single authentication protocol is universally superior; each serves different use cases with varying strengths:

• OIDC: Best for modern web and mobile applications requiring user authentication
• SAML: Still dominant in enterprise environments with complex requirements
• Kerberos: Excels in Windows domains and internal network authentication
• LDAP: Primarily a directory service that can support authentication
• OAuth 2.0: Focused on authorization rather than authentication

Modern applications often implement multiple protocols to satisfy different requirements and integration scenarios. The trend is toward OIDC for new development, with SAML remaining important for enterprise integration, Kerberos for internal network auth, and LDAP as a directory backend.