If you describe something as authentic, you mean that it is such a good imitation that it is almost the same as or as good as the original.
patterns for making authentic frontier-style clothing.
制作地道的边疆风格服装的图样。
An authentic piece of information or account of something is reliable and accurate.
I had obtained the authentic details about the birth of the organization.
我已经弄到了有关该组织成立的可靠的详细资料。