In the context of authentication and authorization, the term “token” is a broad concept that encompasses various types of tokens, including access tokens.

A token : is a piece of data that represents an identity, authentication, or authorization claim. It is a digital credential that is used to prove the authenticity of a client, verify permissions, or gain access to protected resources. Tokens can take different forms and have different purposes based on the specific use case or protocol.

An access token : is a specific type of token that is used for authorization purposes. It is granted to a client by an authorization server after successful authentication. The access token is then presented by the client to access protected resources, such as APIs or web services, on behalf of the authenticated user.

Thus an access token is a specialized type of token that is specifically used for authorization, whereas the term “token” can refer to a more general concept that encompasses various types of tokens used in authentication, authorization, and identity management.

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Access token types can vary depending on the authentication and authorization mechanism being used. Here are some commonly encountered access token types:

An identifier type access token, also known as a reference token : is a type of access token that serves as an identifier or reference to the actual authorization information stored on the server. Instead of carrying the complete authorization details directly within the token, it acts as a pointer or key to retrieve the relevant information.

Here are some characteristics of identifier type access tokens:

1. Opaque Identifier: An identifier token is typically an opaque string or value that does not reveal any meaningful information about the authorization. It is not self-contained and doesn’t carry any explicit claims or data.
2. Lookup Mechanism: When an identifier token is presented to a server or resource, it needs to perform additional steps to validate and retrieve the associated authorization information. This may involve querying a database or making API calls to an authorization server.
3. Server-Side Authorization Storage: The server that receives the identifier token needs to maintain a storage mechanism to map the token to the corresponding authorization details. The token acts as a key or reference to the authorization information stored on the server-side.
4. Flexibility and Control: The use of identifier tokens provides flexibility in managing and controlling authorization information. It allows the server to maintain and update the authorization data independently of the token itself. Changes in the authorization information can be reflected by updating the server-side storage.
5. Reduced Token Size: Since the identifier token doesn’t carry the complete authorization information, it can be relatively smaller in size compared to self-contained access tokens. This can be advantageous when transmitting the token over the network or when storing it in memory.

A self-contained access token is a type of access token that carries all the necessary authorization information within the token itself. In other words, the token is self-sufficient and contains all the relevant claims or data required to authenticate and authorize the client.

Here are some key characteristics of self-contained access tokens:

1. Authorization Information: A self-contained access token includes the necessary claims or data that describe the client’s authorization, such as user identity, permissions, roles, or any other relevant details. These claims are typically encoded within the token.
2. Compact and Portable: Self-contained access tokens are designed to be compact and portable. They can be easily transmitted between parties as a single entity without the need for additional lookups or dependencies on the server-side.
3. No Additional Calls: When a self-contained access token is presented, the server can validate and authorize the token without making additional calls to an authorization server or external resources. All the necessary information to perform the validation is contained within the token itself.
4. Verification: The server can verify the authenticity and integrity of a self-contained access token without relying on external systems. This is usually done by verifying the token’s signature or using a pre-shared secret or public-private key pair.
5. Reduced Server-Side Storage: Since the authorization information is embedded within the token, self-contained access tokens do not require extensive server-side storage to maintain the state of the token. The server can validate and authorize the token based on its internal claims.

Here is a table that summarizes the differences between identifier type access tokens and self-contained access tokens:

Feature	Identifier Type Access Token	Self-Contained Access Token
Opaque	Yes	No
Information stored by authorization server	Identifier only	Scope, identity of user who issued the token, and any other information that the authorization server wants to include
Information needed by resource server	Scope and identity of user who issued the token	None
Contact with authorization server	Required	Not required

In general, self-contained access tokens are more efficient than identifier type access tokens. This is because self-contained access tokens do not require the client to contact the authorization server to get information about the access token. However, self-contained access tokens are also more complex to implement.

The following are some of the factors that you should consider when choosing between identifier type access tokens and self-contained access tokens:

• Performance: Self-contained access tokens are more efficient than identifier type access tokens.
• Complexity: Self-contained access tokens are more complex to implement than identifier type access tokens.
• Security: Self-contained access tokens are more secure than identifier type access tokens, because they do not require the client to contact the authorization server to get information about the access token.
• Support: Not all authorization servers support self-contained access tokens.

Ultimately, the best choice for you will depend on your specific needs.

Access tokens serve as powerful tools in establishing secure and controlled access to protected resources. Their role in authentication and authorization cannot be overstated. By leveraging access tokens, applications and APIs can enhance security, protect sensitive data, and establish granular authorization mechanisms. Understanding the various types of access tokens and implementing appropriate security measures is crucial for building robust and reliable systems in the digital age.