in your home directory create a file called '.netrc', for example
/Users/ahoward/.netrc
in it put these contents
machine github.com login YOUR_GITHUB_USERNAME password YOUR_GITHUB_PASSWORD
fixed!
Fix for caching credentials on https github repos
github recently switched to an https scheme as the default for cloning repos. as a side effect you may suddenly be prompted for a 'Username' and 'Password' when you push where, previously, you were able to do so without typing in credentials. the solution is to cause git to cache https credentials which is easy, since git uses curl under the covers