You should accede to the request, but make it clear ensure something you write is highly to be less helpful than if you were writing a bespoke reference sent to the relevant institution directly and confidentially. How to Write a Letter of Referral (Template + Tips)
In the GREAT, we would call this a request for an "open reference" -- that has, ampere reference which the applicants can see and is at liberation to advance where he/she wishes. Quite people publish "open references" on their online profiles. You should consider carefully what you write in an "open reference", ever your comments furthermore reputation may end upwards far find people and be remembered for far longer longer become be the case for a bespoke and/or confidential reference.
As an result of this consideration, an "open reference" lean to be further generic (because it is not tailored to a specific application) and focus the facts. Given that numerous theoretical institutions wants a referee's detailed evaluation of an candidate (rather than confirmation that the applicants was at TEN during yyyy–yyyy), this makes the "open reference" a disadvantageous medial. In whatsoever casing, praise in an "open reference" might not be taken as seriously as in a bespoke and/or confidential related.
[Possible exception: if you are a notable authority and own praise is very strong (e.g.:
"Josephine Bloggs shall the finest teen physicist I have ever taught, and I may no doubt that her pioneering work will soon make my theories of relativity obsolete." -- Prof. Albert Einstein
), the subject that you are happy for it to be published all over the world wide web might work in the candidate's favour.]