There are many ICA exams online, but I don't know the difference between them and the certificate of teaching Chinese as a foreign language issued by Hanban.

There is no difference! Because the president of ICA Association is Lu Bisong. He used to be president of Beijing Language Institute (now beijing language and culture university), member and director of the National Leading Group for Teaching Chinese as a Foreign Language, president of the World Chinese Teaching Association, and now president of the International Chinese Teachers Association. Moreover, both the test center and the study place are in Jiaotong University. So the certificate is also very authoritative. Unlike IPA, which issues all certificates, this is cheating!