Access Token

1. what is an access token?

An access token is an authentication token that enables a client to access protected resources on a server after the user has been successfully authenticated. This is part of the OAuth 2.0 specification for authorization.

1.2 What are Access Tokens used for?

Access tokens serve as digital keys that allow applications to act on behalf of a user without knowing their login details.

2. how do access tokens work?

2.1 How access tokens work

Access tokens are central components in modern authorization systems, especially in the context of OAuth 2.0 and OpenID Connect. They allow clients to securely access server resources after the user has been successfully authenticated and authorized. Here is a detailed explanation of how Access Tokens work:

2.2 Token issue

1. User authentication: The process begins with the authentication of the user with an authorization server. This can be done through various methods, including password-based logins, multi-factor authentication or even biometric methods.
2. Authorization request: After authentication, the client sends an authorization request to the server. This request usually contains the desired scope of access, the client identifier and, if applicable, a redirect URI to which the server can send the user after successful authorization.
3. Approval by the user: The user must approve the request, in particular the scope of access requested by the client. This is an essential step to ensure that users have control over what data and functions are made accessible.
4. Token output: After successful authentication and authorization, the Authorization Server generates the Access Token. This token contains information that identifies the user and the authorized scope and is digitally signed to prevent tampering.

2.3 Use of access tokens

1. Token transmission: The client receives the access token and can use it in subsequent HTTP requests to access protected resources. The token is typically transmitted in the Authorization header as a Bearer Token.
2. Resource access: For each request with an access token, the resource server checks the token for validity, including verification of the digital signature, the issuer and the expiration date. The server also checks whether the authorizations of the token match the requested access.
3. Token expiration and renewal: Access tokens are usually only valid for a limited time, which reduces the risk of misuse if they are compromised. If a token expires, the client can use a refresh token, if available, to obtain a new access token without the user having to re-authenticate.
4. Token revocation: In some cases it may be necessary to revoke a token prematurely, for example if it is suspected that the token has been compromised. Such revocation mechanisms require additional implementations on the Authorization Server.

2.4 Security mechanisms

• HTTPS: All data exchange involving access tokens should take place via HTTPS to protect the data from interception and manipulation.
• Short lifespan: The limited validity period of access tokens helps to limit the security risk.
• Scope restriction: The use of scopes makes it possible to restrict access to what is strictly necessary.

3. security aspects of access tokens

Access tokens are essential for security in modern authentication systems, as they enable direct access to protected resources. Here are some specific security aspects and practices that need to be considered when using Access Tokens:

Short service life

1. Risk minimization: The short lifespan of access tokens is a core strategy to minimize the risk posed by a possible compromise. A short expiry interval limits the time window in which an intercepted or otherwise misused token can be used.
2. Typical validity period: Access tokens are usually valid for between one hour and one day. This time span offers a compromise between user-friendliness and security requirements.
3. Dynamic adjustment: In security-critical applications, the lifetime of tokens can be dynamically adjusted based on the risk profile of the transaction or user.

Security practices

1. Secure transmission:
   • HTTPS: All communication involving access tokens must take place via HTTPS to protect the data from eavesdropping and man-in-the-middle attacks. HTTPS encrypts the entire data exchange between client and server.
   • Tokens in authorization headers: Access tokens should be transmitted in the Authorization header as bearer tokens to avoid exposure in URLs or log files.
2. Secure storage:
   • Client-side security: On the client side, tokens should be stored in secure storage such as secure storage in mobile operating systems or in encrypted cookies in the browser.
   • Avoid local storage: Tokens should not be stored in local storage or other easily accessible storage areas in web applications, as these areas are susceptible to XSS attacks.
3. Token validation:
   • Server-side controls: Servers should implement mechanisms for the immediate invalidation of tokens, which can be activated if misuse is suspected.
   • Proactive monitoring: Systems should be monitored for unusual activity that could indicate the misuse of tokens, such as atypical request patterns or access from unusual geolocations.

Additional safety considerations

• Cross-Origin Resource Sharing (CORS): CORS policies should be strictly defined to prevent malicious websites from accessing tokens.
• Token binding: Newer technologies such as token binding can further enhance security by binding the token to specific characteristics of the client, reducing the risk of token reuse by attackers.

These security measures are critical to ensure the integrity and confidentiality of access tokens and to ensure that they can fulfill their role as secure intermediaries for authentication and authorization.