So Apache OLTU does not come with any user support. Any bugs that might show up on using it with the OAuth module would have to be fixed by us.
After discussions with Harsha, Suranga and on Talk, we have decided to give Spring Security OAuth a go. There are compatibility issues when using this project with Spring 3.1 or lower, hence supporting spring security oauth on openmrs 1.10 and lower is going to be a challenge.
As of now, I am working on completely providing OAuth2 support on openmrs 1.11.x and above by integrating spring security oauth project. Once done, I will proceed on extending this support to 1.9.x and 1.10.x so that OAuth2 module can work in parallel with the FHIR module