Authentic means Good
It seems to me that the word authentic is ubiquitous in the learning sciences literature. Yet, I get the feeling that it just means good.
Certain words have the property of meaning multiple things. When these words are used in an ambiguous context what they really mean is good.
About half of the time, the writer doesn't know how to make the argument, so they just throw the ambiguous word in front, because nobody will disagree with good. For example, an authentic replica is not the real thing (i.e. one meaning of authentic). Instead replicators realize that authentic means good and it obscures people from really seeing that a replica is a fake.
The other half of the time, the writer does have something significant to say, but gets drawn in by the buzz-word quality of the word. So, instead of saying what they really mean, they say the ambiguous word. In those cases, it would be better if they instead gave the meaning. For instance, you could say that Learning by Design is an authentic way of teaching science. What you might really be trying to convey is that the children in a Learning by Design classroom are learning science through a similar process of experimentation that prototypical scientists use. Sure, there are some good vibes that come from the ambiguous phrase, but it really doesn't tell you much.
Authentic is one of those buzzwords. In learning, it is the worst culprit. Concrete, transfer, and collaboration are other ones. The concepts aren't bad. You just should use the specific definition when making your points.
Outside of learning, object-oriented is another example. Most "right-thinking" people agree that object-oriented is good, but they differ on what it means. I personally prefer authentic object-oriented programming.