What Is a SOAP API?

SOAP is a standards-based messaging protocol specification. SOAP messages exchange structured information using XML as the message format. In a nutshell, a SOAP message is essentially an XML document that consists of four different elements:

• SOAP envelope: establishes the XML document as a SOAP message
• SOAP header: includes information on the header details
• SOAP body: includes information on the SOAP requests and the responses
• SOAP fault: includes information on any errors that occur

With SOAP, an application can invoke a web service, send or retrieve data, or issue a procedure call. A SOAP message travels using application-layer protocols like Hypertext Transport Protocol (HTTP), though it can also run on Simple Mail Transfer Protocol (SMTP), Java Message Service (JMS), and others.

Despite the stigma that SOAP carries of being an outdated technology, its longevity and long track record of use would actually imply that the protocol is quite effective. Let’s take a look at a few of the notable benefits of using SOAP:

• Compatible with all programming languages. Due to the fact that SOAP is rooted in the XML format, it is interoperable with all programming languages and provides a standardized way of exchanging data between different software systems. This means that developers can create applications that can access data from different sources.

• Perfect solution for working with multiple extensions. With WSDL, for example, a developer gets the information they need to develop and implement a SOAP API with relative ease. SOAP’s multiple extensions, like WS Addressing, WS Security, and WS Federation, are also helpful as pre-built app components.

• A way to exchange data in a secure and reliable manner. While both SOAP and REST APIs can utilize HTTPS (SSL/TLS) for encryption, SOAP has additional built-in security features through WS-Security standards. These features provide advanced security capabilities beyond transport-layer encryption, such as message-level security, encryption, and digital signatures.

On the downside, SOAP has shown some pretty clear weaknesses when compared to some of the newer-generation protocols. Let’s review some of the key disadvantages of using SOAP vs. protocols like REST or GraphQL:

• SOAP is comparatively complex and time-consuming. The SOAP syntax tends to be challenging compared to its RESTful alternative. Performance can be an issue because parsing XML data can be CPU- and memory intensive.

• “Language-agnostic” format comes with strings attached. And while SOAP is theoretically vendor-neutral, implementing it often involves committing to a stack, such as Microsoft, which not everyone wants to do.

SOAP creates some exposure to cyber risk as well. SOAP API cybersecurity vulnerabilities include denial-of-service (DoS) attacks, ‍XML injection, ‍SQL injection, command injection, and more. SOAP is also vulnerable to spoofing and man-in-the-middle (MITM) attacks. Web service security tools can mitigate many of these risks.

Use of SOAP and the web services standards has been in decline since the emergence of Representational State Transfer (REST) as the primary basis for APIs, data exchange, and web application integration. There’s an idea that REST “replaced” SOAP. This is true, in a limited way, but it’s worth noting the differences between the two.

• SOAP is a protocol, in contrast to REST, which is an architectural style
• SOAP uses web services to expose functionality to clients, versus REST, which relies on URLs to access components of a REST service
• SOAP requires more bandwidth than REST
• SOAP works exclusively with XML formats, versus REST, which can work with XML, plain text, XML, Hypertext Markup Language (HTML), and JavaScript Object Notation (JSON)
• SOAP cannot use REST, but REST can use SOAP

SOAP and GraphQL are two different protocols that are used to communicate with web services. They both have their own advantages and disadvantages, but they are both widely used today. SOAP is a request-response protocol that uses XML for the request and response.

GraphQL, on the other hand, has been gaining popularity over the years because it offers more flexibility than SOAP. One of the most notable advantages is that it provides a way to query data from multiple sources without having to use multiple APIs. It also allows for better performance because it doesn’t require XML parsing or serialization.

SOAP integrates the WS-Security functionality. Using these protocols, we can determine security measures in transactions and provide privacy guidelines for data integrity in a transactional environment. A further advantage is that it supports encrypted and cryptography signed documents. WS-Security allows your message to not just have HTTPS encryption but also have authentication data in a message. It must also ensure that the data whose transits outside the HTTPS protocol are retrieved only by the correct processing on that server and not by the correct server itself.

The REST API only supports HTTP security methods. If applications send messages using an HTTPS connection, then this message can only be secured by HTTPS communication. This means that the message is encrypted only at the time of transport from customer to services. It works well for public websites. Because REST APIs don’t feature security capabilities and extension capabilities as SOAP APIs do, security depends upon the API’s own architectures. A REST API can have a specific security mechanism that allows only authenticated users to access it.