Authentication Explained: When to Use Basic, Bearer, OAuth2, JWT & SSO

Authentication has always been one of the most important pillars of software development. From the earliest web applications to today's complex ecosystems of microservices, APIs, and cloud platforms, the question remains the same: how do we verify who someone is, and what they are allowed to do?

The challenge is that authentication is not a one-size-fits-all problem. Different use cases require different solutions, and over the years, several approaches have become popular. In this article, we will take a deep dive into five common authentication methods: Basic Authentication, Bearer Tokens, OAuth2, JWT, and SSO. We will cover how they work, their advantages and disadvantages, and when to use each.

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Basic Authentication

Basic Authentication is one of the earliest methods defined in the HTTP specification. In this approach, every request includes an Authorization header containing a Base64-encoded string of username:password.

How it works

Authorization: Basic dXNlcjpwYXNzd29yZA==

The server decodes the header, checks the credentials, and decides whether to grant access.

// Client-side implementation
const username = 'user';
const password = 'password';
const credentials = btoa(`${username}:${password}`);

fetch('/api/data', {
    headers: {
        'Authorization': `Basic ${credentials}`
    }
});

Advantages

• Extremely simple to implement
• Supported out-of-the-box by most HTTP clients, browsers, and servers
• No additional infrastructure required
• Stateless nature eliminates session management complexity

Disadvantages

• Insecure if used without HTTPS, as credentials can be intercepted
• Credentials are sent with every request, increasing exposure risk
• No built-in mechanism for session expiration or revocation
• Base64 encoding provides no real security, just obfuscation

When to use Basic Authentication

Use Basic Authentication when:

• Building prototypes or quick internal tools where speed of implementation matters more than security
• Working with legacy systems that only support Basic Auth
• Creating simple administrative interfaces with additional network-level security
• Developing internal APIs within a secure network perimeter

Avoid Basic Authentication for:

• Public-facing applications
• Mobile applications
• Systems handling sensitive data
• Applications requiring session management

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Bearer Token Authentication

Bearer Token Authentication separates the authentication step from the authorization step. Instead of sending username and password with each request, the client includes a token in the Authorization header.

How it works

The flow involves two phases:

1. Authentication: Client sends credentials once to get a token
2. Authorization: Client uses token for subsequent requests

Authorization: Bearer abc123xyzToken

// Login to get token
async function login(username, password) {
    const response = await fetch('/auth/login', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ username, password })
    });
    const data = await response.json();
    return data.token;
}

// Use token for API requests
async function fetchData(token) {
    const response = await fetch('/api/data', {
        headers: {
            'Authorization': `Bearer ${token}`
        }
    });
    return response.json();
}

Advantages

• More secure than Basic Auth since credentials are not repeatedly exposed
• Tokens can be short-lived, renewable, and revoked instantly
• Supports fine-grained access control through token scoping
• Enables better session management and monitoring

Disadvantages

• If a token is stolen, the attacker can use it until it expires
• Requires a token management system for issuing, storing, and validating tokens
• Additional complexity compared to Basic Auth
• Requires secure token storage on the client side

When to use Bearer Tokens

Use Bearer Tokens when:

• Building APIs that need lightweight and secure token-based access
• Developing microservice architectures where services communicate via tokens
• Creating mobile and web apps that require session-like authentication
• You need the ability to revoke access immediately

Avoid Bearer Tokens when:

• You need completely stateless authentication (consider JWT)
• Building simple internal tools where Basic Auth suffices
• Token management overhead exceeds the security benefits

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OAuth2

OAuth2 is not simply an authentication method; it is a framework for authorization. It enables delegated access by allowing a user to grant a third-party application access to resources without sharing their password.

How it works

A common OAuth2 Authorization Code flow:

1. The user logs into an authorization server (e.g., Google)
2. The third-party application requests access to the user's resources
3. The authorization server issues an access token to the application
4. The application uses this token to call APIs on the user's behalf

// Redirect user to authorization server
function initiateOAuth() {
    const authUrl = `https://accounts.google.com/oauth/authorize?` +
        `response_type=code&` +
        `client_id=${CLIENT_ID}&` +
        `redirect_uri=${REDIRECT_URI}&` +
        `scope=profile email`;

    window.location.href = authUrl;
}

// Exchange authorization code for access token
async function exchangeCodeForToken(authCode) {
    const response = await fetch('/token', {
        method: 'POST',
        headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
        body: new URLSearchParams({
            grant_type: 'authorization_code',
            code: authCode,
            client_id: CLIENT_ID,
            client_secret: CLIENT_SECRET,
            redirect_uri: REDIRECT_URI
        })
    });
    return response.json();
}

Key concepts

• Authorization Server: Issues tokens after authenticating the user (Google, Facebook, GitHub)
• Resource Server: Validates tokens and serves protected resources
• Scopes: Define what permissions are being requested (read profile, access email, etc.)
• Grant Types: Different flows for different client types (web apps, mobile apps, server-to-server)

Advantages

• Passwords are not shared with third-party applications
• Supports fine-grained permissions through scopes
• Widely adopted across major platforms and services
• Enables secure third-party integrations
• Users maintain control over what data is shared

Disadvantages

• Implementation complexity requires understanding multiple flows
• Security issues can arise if flows are misused or implemented incorrectly
• Requires coordination between multiple parties (client, auth server, resource server)
• Can be overkill for simple authentication needs

When to use OAuth2

Use OAuth2 when:

• Implementing social login ("Sign in with Google/Facebook/GitHub")
• Building applications requiring third-party integrations with controlled access
• Creating API ecosystems where multiple applications need access to user data
• You need delegated access and fine-grained permissions
• Building mobile apps that integrate with external services

Avoid OAuth2 when:

• You only need authentication for your own application
• Building simple internal tools
• The complexity outweighs the benefits
• You don't need third-party integrations

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JWT (JSON Web Tokens)

JWT is a compact token format that contains encoded information. It usually has three parts: Header, Payload, and Signature, separated by dots.

How it works

A JWT looks like this:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoxMjMsInJvbGUiOiJhZG1pbiJ9.sv9kYlX4...

• Header: Algorithm and token type
• Payload: Claims (user ID, roles, permissions, expiration)
• Signature: Ensures token integrity using cryptographic signatures

// JWT usage example
function parseJWT(token) {
    const [header, payload, signature] = token.split('.');
    return {
        header: JSON.parse(atob(header)),
        payload: JSON.parse(atob(payload)),
        signature: signature
    };
}

// Using JWT for authentication
async function authenticateWithJWT(token) {
    const response = await fetch('/api/profile', {
        headers: {
            'Authorization': `Bearer ${token}`
        }
    });

    if (response.ok) {
        const userData = await response.json();
        return userData;
    }
}

Advantages

• Self-contained: the token carries all information needed for authentication
• Stateless: no server-side session storage required
• Can be verified quickly using the signature without database lookups
• Works well in distributed systems
• Contains user information directly in the token

Disadvantages

• Large tokens if many claims are included
• Difficult to revoke or invalidate before expiration
• Token data is readable (Base64-encoded, not encrypted)
• If not validated correctly, can lead to serious vulnerabilities
• Cannot be updated once issued

When to use JWT

Use JWT when:

• Building stateless authentication in Single Page Applications (SPAs)
• Developing mobile applications that need lightweight, stateless sessions
• Creating microservices that need fast authentication checks without database lookups
• Working in distributed systems where centralized session storage is impractical
• You need to include user information in the token itself

Avoid JWT when:

• You need to revoke tokens immediately
• Tokens would contain sensitive information
• Simple bearer tokens would be sufficient
• You're not comfortable with token contents being readable

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Single Sign-On (SSO)

Single Sign-On allows a user to authenticate once and then access multiple independent applications without re-entering credentials. This is achieved by centralizing authentication with an identity provider.

How it works

SSO typically uses protocols such as SAML, OAuth2, and OpenID Connect to implement the functionality.

// Conceptual SSO flow
// 1. User tries to access Application A
// 2. Application A redirects to Identity Provider
// 3. User authenticates with Identity Provider (if not already)
// 4. Identity Provider sends signed assertion back to Application A
// 5. Application A validates assertion and creates local session
// 6. User can now access Applications B, C, D without additional login

// Example redirect to SSO provider
function redirectToSSO() {
    const ssoUrl = `https://sso.company.com/auth?` +
        `return_url=${encodeURIComponent(window.location.href)}&` +
        `app_id=my-application`;

    window.location.href = ssoUrl;
}

Key components

• Identity Provider (IdP): Central service that handles authentication
• Service Provider (SP): Applications that trust the identity provider
• Assertions: Signed statements about user authentication and attributes
• Trust Relationship: Cryptographic trust between IdP and service providers

Advantages

• Improved user experience: one login grants access to many systems
• Centralized identity and access management
• Simplifies compliance and auditing
• Reduces password fatigue and help desk requests
• Enhanced security through centralized authentication policies

Disadvantages

• Requires dedicated infrastructure and configuration
• If the identity provider is compromised, all connected systems are exposed
• Can become a single point of failure
• Complex setup and maintenance
• Vendor lock-in with specific SSO solutions

When to use SSO

Use SSO when:

• Building enterprise environments with many internal applications
• Creating ecosystems of related products that need seamless navigation
• Organizations want centralized access control and user management
• Compliance requires unified audit trails
• You have multiple applications with the same user base

Avoid SSO when:

• You have only one application
• The infrastructure investment exceeds the benefits
• You lack the technical expertise for proper implementation
• Security requirements demand isolated authentication systems

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Putting It All Together

Choosing the right authentication method depends on your specific context and requirements:

For Simple Applications

• Basic Authentication: Internal tools, prototypes, legacy system integration
• Bearer Tokens: Single applications needing better security than Basic Auth

For Modern Web Applications

• JWT: SPAs and mobile apps requiring stateless authentication
• Bearer Tokens: Applications needing token revocation and management flexibility

For Third-Party Integration

• OAuth2: Social login, API access delegation, third-party app permissions

For Enterprise Environments

• SSO: Multiple applications, centralized identity management, enterprise security

Security Considerations

• High security needs: Avoid Basic Auth, consider Bearer Tokens or SSO
• Immediate revocation required: Avoid JWT, use Bearer Tokens or SSO
• Distributed systems: JWT or OAuth2 depending on requirements

Remember that these methods can be combined. For example, OAuth2 can use JWT tokens, or SSO can be built on top of OAuth2. The key is understanding each method's strengths and limitations to make informed decisions for your specific use case.

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Conclusion

Authentication is one of the hardest and most important aspects of software development. It requires balancing security, usability, and complexity. By understanding how Basic Auth, Bearer Tokens, OAuth2, JWT, and SSO work, and by recognizing their trade-offs, you can make informed decisions for your applications.

Do not choose a method just because it is trendy or widely used. Choose it because it matches your project's requirements, security needs, and complexity constraints.