Although full service oriented architecturesecurity maturity is yet to come, 30 percent of organisations now use SOA for external integration with customers and partners.

For standard Web services using SOAP, WS-Security has achieved critical mass as a foundational standard. On the other hand, advanced SOA security - involving federation among partners, nonrepudiation, and propagation of user identities across multiple layers of service implementations - is in its early days.

To navigate the path from what's practical today to the future of advanced SOA security, establish an iterative design process for evolving your SOA security architecture that considers your current and future security requirements, emerging industry specifications, overlaps in product functionality for SOA security, and possibilities for custom security integration.

As a baseline for designing SOA security, the simplest way to secure SOA requests and responses is to place them within a virtual private network (VPN). The most common method for external SOA security is two-way Secure Sockets Layer (SSL), which: 1) allows each of the communicating partners to authenticate the other, and 2) sets a high bar for security: Hackers cannot even connect to an SOA-based service unless they steal a certificate and key from a service consumer.

Although VPNs are relatively easy to establish, VPN-based SOA security is coarse-grained and offers no ability to support advanced functions such as: propagation of user identity across multiple layers of service implementations; coordination and federation among multiple security domains; and strict nonrepudiation. Also ongoing management of certificates can be an administrative burden.

Other major alternatives for SOA security include leveraging existing SOA security features in Java or .NET application platforms and concentrating SOA security within an SOA specialty product such as an enterprise service bus, SOA and Web services management solution, SOA security server, or SOA appliance. Appliances provide the simplest and most focused "drop-in" solution for SOA security, but there are intricate trade-offs to consider among the SOA specialty products as you build your overall SOA platform.

Even with the emerging features of application servers and SOA specialty products, simple SOA security solutions can be compelling, Historically, organisations have been reticent to tackle the difficulties of implementing advanced application security requirements. As SOA security implementations mature - along with broader architectures for security federation - it will become easier to implement advanced security scenarios.

Many user organisations will find that advanced SOA security becomes mandatory - especially with increasing data privacy and other regulations. Thus it is important, even if you start with a simple SOA security solution, to anticipate the need for and leave paths open to build additional, deeper security functionality as business requirements demand and SOA security maturity allows.

Forrester strongly recommends that you design a solution that does not require application developers to do security-related coding. Even with strong guidelines and code reviews, embedding security into application code is risky both in terms of achieving consistent security and of allowing future flexibility and enhancement of application security.

Note that keeping developers from having to write code for security does not eliminate the need to train application developers to use secure coding practices. Secure coding is a separate realm of application security practice, involving concerns such as ensuring that application failures do not open security holes.

Finding the right combination of industry standards, products, integrations, and frameworks for your security strategy is an iterative process where you:

1. Identify Your Security Requirements. Assess your requirements against a broad, strategic list of security functions. This forms the foundation for designing your SOA security strategy and solution. Organise requirements according to the major design focal points of your SOA-based solution.

Forrester uses a model organised around the service consumer, the request-response, the service provider, and the security environment. As you continue through the iterative process for SOA security design, you may have to reconsider selected requirements as you learn more about standards, products, and your organisation's ability to pay for the SOA security your requirements imply.

2. Determine Your Use of SOA Security Specifications. Your SOA security requirements set the stage for determining the range of SOA security specifications that might meet your requirements. When choosing the actual specifications you will use, however, you must account for which specifications the products in your infrastructure (existing products, plus new ones that you may buy for SOA) will support.

Core specifications include WS-Security, WS-I Basic Security Profile, XML Encryption, and XML Signature. Advanced specifications include WS-Trust, WS-SecurityPolicy, WS-Federation, XACML, and WS-SecureConversation.

3. Select the Products that will Provide Your Core SOA Security Functions. Many functions within an SOA security solution, such as performing authentication using WS-Security headers, can be performed by multiple product types in different product categories. Your design process will have to consider each option, assess the trade-offs, and select one product (or a coordinated set of products) to provide the core functions for SOA security.

Key product categories that might contribute to your SOA security solution include: SOA appliances, SOA management solutions, enterprise service buses, SOA security servers, application servers, security token servers, entitlements management servers, and identity and access management solutions.

4. Configure and Integrate Products to Work Together. It's likely that you will have multiple products that perform a given SOA security function, and the products will have to be integrated to work coherently together. Much of this integration may be done with product configuration options (e.g., configuring an SOA appliance to delegate authentication to a particular single sign-on product), but it may require building integration components using product programming interfaces.

5. Fill in the Holes with Frameworks. After the product integration is done, it may be useful to build helper frameworks for application developers so that they will not have to write security code within their SOA-based applications.

Forrester recommends using an iterative process for two primary reasons. First, typically not all applications need all of your security requirements; initial applications may be able to do with a lighter-weight pass on building your SOA security solution, while later applications require you to fill in your solution with additional features. Second, each time you make a pass through, you will learn more about how to build the most effective SOA security solution with the pieces that you have.

SOA leaders are still paving the road for the rest to follow. For some organisations, there may be a business scenario where advanced security has a high value. Such organisations can justify the cost of building advanced SOA security solutions. These leaders will, along the way, help solidify industry specifications and help vendors mature their products.

If your organisation is one with immediate needs for advanced SOA security, there are many available products and standards to build on, but proceed with caution: You should build extra time into project plans for prototyping, product debugging, and performance and scalability testing.

Randy Heffner is a Vice President at Forrester Research, serving Enterprise Architecture professionals. He is a leading expert on architectures and design approaches for building enterprise applications that are secure and resilient in the face of continuous business and technology change.