I largely agree with comments by Tobias Kildetoft, JeffE, and Nicole Ruggiano, but there's another angle that has not been considered, namely, the supervisor might be acting in the OP's best interests.
THIS ANSWER IS CONTROVERSIAL. At the time of adding this remark, down-votes outweigh up-votes. The comments suggest that down-votes are due to the supervisor being presumed guilty of malpractice. This is a serious, worrisome accusation. Let's step-back momentarily and presume innocence.
The OP has stated that their supervisor wants his post-doc to review a paper co-authored by the OP and OP's previous supervisor. It has been assumed that the supervisor is acting in his own interests. This might not be the case. Perhaps the supervisor believes the paper can be improved, after review. The OP should assess whether this might be the case. If so, then the OP should consider whether such improvements are worth adding the supervisor and post-doc as co-authors. They might well be worth it. For instance, if the improvements enable publication at a more prestigious journal, then I'd consider such improvements worth adding the supervisor and post-doc as co-authors.
I fully appreciate that reviewing is insufficient for authorship and, as I have hinted, I fully agree with Tobias Kildetoft, JeffE, and Nicole Ruggiano, if the supervisor wants co-authorship without contribution. That's not the issue I want to address; I want to establish whether the OP has fully understood the supervisor's intent. In particular, I want to establish whether the supervisor/post-doc is also offering a scholarly contribution. If so, then the OP should consider co-authorship.
(In using the phrase "feels like," the OP is hinting that the supervisor's intent is unclear. Hence, the need for clarification and the potential importance of this response.)