In this answer it is claimed that authorship is given away for "free" in some fields (e.g., obtaining the funding). The comments to the answer suggest that this is field dependent. I am looking for documentation from a field that suggests that authorship can be given away for "free". For example, the ICMJE has authorship guidelines that put a pretty high bar on authorship. Is there any documentation that suggests that supervising a student or getting funding is enough to warrant authorship?
Short answer: free authorship, also known as gift authorship, is a clear violation of research and publication ethics. The limit between “small contribution” and “no contribution” is not, however, easily defined; different fields put it at different levels.
I don't think the answer actually states that. It lists a series of contributions that are, in some field, considered important enough to warrant (in some combinations) authorship on resulting papers:
they get grant money, they train you to use the lab, they train you to do statistics... or they might make suggestions for the research design, the main theoretical focus of the presentation / manuscript
All journals (or publishers) have policies or guidelines on how authorship should be determined. In all cases, it involves significant scientific or technical contributions to the work published. Authorship determination has to be weighted in each individual case, as no two situations are identical (and not simple rule of thumb can encompass all possible situations, as Peter Jansson highlights).
There are so many ways in which people can contribute to an intellectual work, such as a research project and academic papers. It happens that different fields of research have different habits in authorship determination, giving more or less weight to different types of contributions. My own background is in physics and chemistry, where authorship tend to be more generous that, say, computer science or mathematics. I'll thus argue two examples of what you (and some fields) may consider dubious basis for authorship, but which in my field would be considered fairly standard:
Getting funding. In this age, getting funding most often requires writing a grant proposal for a specific research program, with good and novel ideas, and convincing a tough crowd of other scientists (in a competitive environment) that your program is a good use of taxpayers' money. Thus, in most cases, the person who provides the funding also provides a clear scientific contribution: they identified an important problem to be solved, and provided a general framework for solving it. That's an important part of research! Identifying the right question to ask yourself is half of the job, it is known. (Yeah, I'm trying my hand at Dothraki style in academic context. By the way, thank you for reading so far down my answer.)
Supervising. Whether or not the supervisor actually provided the student with the research project in the first place, supervision implies guidance of the student, which is definitely a scientific contribution. The supervisor will, in many cases, provide a broader view of the field and ideas for related problems relevant to the research, scientific background, and advice on how to use one's research time most efficiently. All of that is highly valuable, and contributes to the publication.
(I've read somewhere “but the supervisor is paid for this, it's his job, so he shouldn't be awarded authorship” — that's plain stupid, pretty much everyone gets paid to do research, thus by that argument most papers would be authorless.)
In both cases, funding and supervising imply scientific contributions, which are the reason for authorship.
I would argue that the Vancouver Protocol is something most people understand but traditions, peer pressure etc. is what makes co-authorship a sometimes fuzzy decision. So as for documentation, I doubt any exists that is accepted by all. That said, I know that in large consortias such as in physics, for example, accelerator work, one signs a contract that automatically adds your name to all papers produced within a given time frame depedning on your time period involved in the project. Such consortia-authorships usually use the consortia name as author with a separate listing of individuals. The consortia-authorship is something I do not think the writers of the Vancouver Protocol had in mind.
Here is an example from from CERN.
In the case of large research groups this type of "contract" (specific in each case) could be a way to officially outline the policy accepted by participants.
This is going to depend on the field. For most fields, the norm is that an author has made "intellectual contributions" to the work. ICMJE updates this requirement to "substantive" intellectual contributions, but most conferences and journals have a written or implied cut-off for how substantive an intellectual contribution is. Many journals and conferences now ask for detailed list of contributions by the authors to combat vanity authorships.
In some fields, for example my own field of Chemistry, the norm is that the individual who has secured the funding has written one or more grant proposals specific to this project. These proposals may have been written with or without the assistance of the students working on the project. They may have even been written before the student joined the project. In chemistry, the proposal needs to be pretty specific about what types of problems will be examined and what methods will be used. Writing the proposal to get the funding is a substantive intellectual contribution counting as "substantial contributions to conception and design" as far as the ICMJE is concerned.
Funding does not necessarily happen this way in every field. As Peter Jansson suggests, a National Lab, consortium, or other funded research center or institute may have a budget process that is separate from the conception and design of experiments. In such a case, the director of the center, whose duties likely include making sure the center is funded, is probably not an author.
Normal behavior for whether the supervisor is an author has been established in every field. Ask your colleagues. Consult your journals/conferences. For example, the American Chemical Society has the following description in their Publication Ethics (Page 3) (emphasis mine):
The co-authors of a paper should be all those persons who have made significant scientific contributions to the work reported and who share responsibility and accountability for the results. Authors should appropriately recognize the contributions of technical staff and data professionals. Other contributions should be indicated in a footnote or an “Acknowledgments” section. An administrative relationship to the investigation does not of itself qualify a person for co - authorship (but occasionally it may be appropriate to acknowledge major administrative assistance). Deceased persons who meet the criterion for inclusion as co-authors should be so included, with a footnote reporting date of death. No fictitious name should be listed as an author or coauthor. The author who submits a manuscript for publication accepts the responsibility of having included as co-authors all persons appropriate and none inappropriate. The submitting author should have sent each living co-author a draft copy of the manuscript and have obtained the co-author’s assent to co-authorship of it.
To the ACS, the individual who takes responsibility for the validity of the data and the work (usually the student's supervisor in chemistry) is an author, even if that person did not design the experiments, collect the data, interpret the results, or write the manuscript. The supervisor has a more permanent position than the student and is likely to be easier to reach with questions five years from now than the student.