This seems to fall under "Installation Information" according to the GPL v3 license. "Installation information" doesn't need to be provided as source code, but it must be provided in such a way that others can take the source code, modify it, and make it work with the "Installation Information" that is provided.
(Technical: At the place where the passwords and secure keys are entered in the source code, I would modify the code so that it doesn't build, followed by instructions how to create your own passwords and secure keys. So you try to build the program, it fails, it points you to instructions, you follow the instructions and change the source files, you try to build again, and it works).