  Authentication is a critical security feature for confirming the identity of
a system's users, typically implemented with help from frameworks like Spring
Security. It is a complex feature which should be robustly tested at all stages
of development. Unit testing is an effective technique for fine-grained
verification of feature behaviors that is not widely-used to test
authentication. Part of the problem is that resources to help developers unit
test security features are limited. Most security testing guides recommend test
cases in a "black box" or penetration testing perspective. These resources are
not easily applicable to developers writing new unit tests, or who want a
security-focused perspective on coverage.
  In this paper, we address these issues by applying a grounded theory-based
approach to identify common (unit) test cases for token authentication through
analysis of 481 JUnit tests exercising Spring Security-based authentication
implementations from 53 open source Java projects. The outcome of this study is
a developer-friendly unit testing guide organized as a catalog of 53 test cases
for token authentication, representing unique combinations of 17 scenarios, 40
conditions, and 30 expected outcomes learned from the data set in our analysis.
We supplement the test guide with common test smells to avoid. To verify the
accuracy and usefulness of our testing guide, we sought feedback from selected
developers, some of whom authored unit tests in our dataset.
