I have been through a 4-year PhD program at my home university. In these 4 years, I have performed several research projects, authored several articles and passed qualification exams. After that, I left for a 3-year academic leave, and found myself ineligible to return to my home university to complete my PhD. I have an option of becoming an external doctorate student at my home university, which will require me to re-take qualification exams to complete my PhD and earn a PhD degree.

However, I am also considering becoming an external graduate student in another country, if this is possible. By saying "external graduate student", I mean a program where non-affiliated scholars might come to a university, present the evidence of their expertise in the field (research articles and a thesis / dissertation), take qualification exams and earn a PhD degree.

Is this an accepted practice in European countries? Are there rules allowing or precluding foreign students from taking these positions?