APIs enable developers to create software programs that interact with servers. They provide a powerful way to innovate, streamline and integrate software applications.
RESTful APIs follow a client-server architectural style that separates the two components to improve scalability and flexibility. These APIs are stateless, cachable and layered with code on demand (optional). They use standard HTTP methods and URIs to communicate with the server.
Communication Model
In general, RESTful APIs communicate with clients and servers using a common language. This guideline is important because many software programs are written in different languages and may have difficulty communicating with one another without an intermediary. Without standardized communication, requests and responses could become a total mess. For example, if a developer receives a response with content that isn’t what was expected — such as text/plain when it was actually intended to be text/css — this might cause the program to fail to display properly.
This communication model uses a uniform interface to ensure that all resources are identified with unique identifiers and have corresponding representations. These are typically delivered via HTTP methods. For example, a request to a collection URI would return a list of the items in that collection. Each item in the list has its own URI that contains information on how to get more details on the individual item.
The RESTful architecture also takes into account that server systems often have a number of additional layers. These layers provide security, handle and distribute traffic, or help with a variety of other functions. This communication model ensures that any interactions between the client application and server are not dependent on layers between them. This allows developers to reorder, update or restructure these server systems without impacting the core request-response interaction between the client and the target server.
Cacheability
The ability to cache responses improves performance, especially during peak usage periods. Caching allows server resources to be reused for repeated requests rather than having to be generated each time, and it saves both processing and network bandwidth.
Caching is typically implemented on the client-side or server-side by using cache directives in the response headers. For example, a GET request can use an ETag to store the hash of the response in a cache; when the same resource is requested again the client looks up the hash in the cache instead of sending a new request to the server.
On the server side, caching is done by setting the Cache-Control header to indicate if the response is public or private, and by adding a Last-Modified or If-Modified-Since header to provide a mechanism for verifying that the cached copy of the response has not changed on the server. Then, the cache can be replaced with a new copy of the response when needed.
The stateless nature of REST makes it a good choice for web services because it separates data storage and application processing concerns, making it easier to scale and manage components in a distributed system. It is also platform- and language independent, enabling developers to work on the UI layer and server layers independently. This helps to speed up development and make it more flexible, which is a key factor in rapid software deployment.
Access Control
The principles that make up RESTful APIs are a key part of the architecture that allows web applications to communicate with each other without using specialized code. When developers adhere to these guiding principles, they can build resilient systems that foster scalability, efficiency, and maintainability over time.
These guiding principles focus on a uniform interface that defines a set of standard HTTP methods (GET, POST, PUT, and DELETE), an identification system for resources with unique URIs combined with representation techniques such as JSON and XML, and a structure that allows users to manipulate resources consistently through those methods. When these principles are applied, they allow the development of APIs that are easy for clients to understand and use, facilitating greater adoption over time.
Another important principle is statelessness, which ensures that each request sent to the server includes all of the data required for it to process properly. This can help reduce the number of calls required for a task, which is critical to improving performance.
REST APIs can be secured with a variety of techniques, including authentication and authorization. This includes using API keys to associate specific permissions with users and implementing security features such as two-factor authentication (2FA) that requires the user to enter a challenge question or provide a biometric identifier when accessing sensitive data.
Security
APIs expose sensitive data over the Internet, making them an attractive attack surface. As organizations replace old SOAP web service APIs with RESTful alternatives, they must incorporate security measures that control their exposure.
Using the same architecture as web applications, RESTful APIs provide a familiar framework for developers. They use URIs to identify resources, which can be accessed and manipulated using standard HTTP verbs like GET, POST and DELETE.
Because they’re stateless by design, RESTful APIs can be used with any programming language that supports HTTP requests. They also allow developers to separate user interface concerns from server components, which improves scalability and manageability.
Security threats can vary depending on the API’s implementation. For example, if credentials and other sensitive information are sent directly in the URLs, they could be leaked by cybercriminals. Also, if the API’s responses contain more information than necessary, it can provide attackers with additional information about the resource or other parts of the system.
To prevent these types of attacks, developers should implement strict validation checks and limit the amount of data returned in a response. They should also enable caching unless the API specifically indicates that this is not allowed. Moreover, they should set up rate limiting so that only a certain amount of traffic can be served in a short period of time to prevent denial-of-service attacks.