Direct Geodesic with Point 2 Azimuth

I am trying to find a way to calculate the direct problem on the WGS-84 ellipsoid but instead of using the initial Azimuth (e.g. lat1, lon1, distance, fwd azi), I want to compute it with the reverse Azimuth (e.g. lat1, lon1, distance, point2-reverse-azimuth).

Are there any tools/libraries out there to do that?

My purpose is to find the tangential latitude to a circle of radius X from any given point to calculate an accurate lat/long bounding box that contains all points within X distance.

Thanks!