Assessment is an essential element in learning processes. It is therefore not unsurprising that almost all learning management systems (LMSs) offer support for assessment, e.g., for the creation, execution, and evaluation of multiple choice tests. We have designed and implemented generic support for assessment that is based on assignments that students submit as electronic documents. In addition to assignments that are graded by teachers, we also support assignments that can be automatically tested and evaluated, e.g., assignments in programming languages, or other formal notations. In this paper, we report about the design and implementation of a service-oriented approach for automatic assessment of programming assignments. The most relevant aspects of our "assessment as a service" solution are that on the one hand the advantages of automatic assessment can be used with a multitude of programming languages, as well as other formal notations (as so-called backends); on the other hand, the features of these types of assessment can be easily interfaced with different existing learning management systems (as so called frontends). We also report about the practical use of the implemented software components at our university and other educational institutions. (Contains 10 figures and 17 footnotes.)