We all know that REST services allow multiple methods for performing different operations on a resource. To avoid any kind of conflicts, RESTful services have to be developed and deployed to ensure that only correct methods are accepted for processing. Other methods automatically are made to get an appropriate error message. The key security attacks are detailed as follows:

• Cross-site request forgery: Resources are being exposed by REST services to the outside, along with a well-designed API. It is crucial to protect PUT, POST, and DELETE request cross-site request forgery (CSRF). The standard protection approach is to use one of the token-based approaches. If there's any cross-site scripting (XSS) in our application, CSRF can still be easily done even if we use random tokens, hence, experts recommend leveraging viable mechanisms to prevent XSS.
• Input validation: We execute validation both on the client and the server side. The client- and server-side script languages have innate capabilities to properly validate requests and responses. If there's an incorrect user input, it's better to reject that. Also, it's better to log input validation failures. If there are more failed input validations, the option to consider is rate limiting the API.
• URL validations: It's possible for attackers to tamper with any part of an HTTP request to break into the employed security methods. The key parts making up an HTTP request include the URL, query string, headers, cookies, form, and hidden fields.
• Secure parsing: All incoming messages have to be systematically parsed for any security violations. It's true that REST can accept messages being framed through multiple mechanisms, including XML and JSON.
• Validate incoming content types: When we use the POST and PUT methods for submitting new data, the client is expected to clearly specify the content-type (such as XML or Java).
• The servers never assume the content type: Servers always have to verify whether the content type and the content are the same. If they don't match, an appropriate error message has to be communicated back.
• Validate response types: This is another validation. REST services allow multiple response types and, hence, the client has to articulate the preferred order of response types in the Accept header, which is part of the request message. Also, there are many MIME types for the typical response types, so clients have to specify which MIME types should be used in the reply message.
• XML input validation: There are XML-specific attacks (XML External Entity and XML signature wrapping) and hence, XML-based services have to securely parse XML messages to be protected against attacks.
• Security headers: To correctly interpret server messages, the server has to embed the content-type header with the correct content type.
• XML encoding: XML messages should be constructed using an XML serializer. Then, only the XML content can be parsed by the browser and be devoid of any XML injection errors.
• Cryptography: When data is getting transmitted, it gets encrypted. That is, the transport-level security (TLS) has to be enabled. TLS is important when credentials, updates, deletions, and any other value-added information get transmitted across. Even experts recommend using mutually-authenticated client-side certificates to guarantee the utmost security to RESTful web services. Similarly, when data gets persisted, the data has to be encrypted, and when data is being used by any application, appropriate security measures have to be in place.
• Message integrity: Cryptography ensures confidentiality, but we need message integrity. That is, we leverage the message digest/hashing algorithms toward message integrity. A JSON web token (JWT) is a standardized, optionally validated, and/or encrypted container format. This is used to securely transfer information between two parties.

API security is an important phenomenon. There is a growing array of best practices and patterns for securing APIs. Collecting error logs comes in handy when visualizing any kind of security implications, In time, this is the surest way forward to guarantee fool-proof security for APIs being designed, published, and maintained.

In conclusion, developers should try to understand the prevailing context and the future. It's not easy to come out with a strategically sound API off the bat. APIs can make or mark the whole scenario if done with passion and discussion. API designers have to start thinking in terms of user perspectives. A robust design is a key factor in producing and sustaining state-of-the-art and multifaceted APIs. A poorly designed API may lead to failure or the customer may not be satisfied with the applications and services.