I have found many different types of midrashic works. Some are, as far as I can tell, accepted as being authoritative. Meaning they were written (compiled?) by the sages in roughly the talmudic era. Examples would be bereshis rabba, midrash tanchuma, pirkei d'rebbi eliezer.
Then there are midrashim that seem to be apocryphal. Such as sefer zerubavel, the sword of Moses and others which seem to be more like fiction based on torah/chazal. They also seem to be of a later origin.
Finally there are some midrashim which seem to be in a gray area, they are not the mainstream but I have seen referenced in traditional rabbinic writing, such as Midrash Abba Gorion, the alphabet of ben sira etc. (there have been termed "smaller midrashim")
I would like to know if there is a list of 'kosher' midrashim. I.e. ones which orthodox judaism has accepted as authentic.