See the answer by Drew for a general description of compiler warnings pertaining to free variables.
In your particular case, however, the culprit is the package
oauth2.el, which for some reason is getting loaded during the byte-compilation of your
user-init-file (perhaps you are a
In this case adding
(defvar foo) to your
user-init-file will not make the warnings go away. Instead, you could try assigning a value to the corresponding variables before the
oauth2 package is loaded in your
(defvar oauth--token-data ())
I removed my suggestion to raise the issue with the
oauth2 package from my answer, as byte-compiling the package on its own does not raise the warnings mentioned. In my case, at least, the warnings only appear because of the way
use-package loads files before byte-compiling user settings, and I'm not entirely sure why, though it's related to the fact that all variables mentioned are void, i.e. they have been defined with
defvar but not assigned a value.