To cite package gfboost in publications use:

Tino Werner (2020). Gradient-Free Gradient Boosting. PhD Thesis, Carl von Ossietzky University Oldenburg URL https://oops.uni-oldenburg.de/id/eprint/4290

Corresponding BibTeX entry:

  @PhdThesis{,
    title = {Gradient-Free Gradient Boosting.},
    author = {Tino Werner},
    language = {English},
    year = {2020},
    school = {Carl von Ossietzky University Oldenburg},
    type = {Dissertation},
    uri = {https://oops.uni-oldenburg.de/id/eprint/4290},
  }