url64 is a small drop-in replacement for the base64 utility that handles URL-safe base64. (With - and _ in place of + and /, and with no padding).
go get github.com/superhuman/url64
To encode:
cat file | url64
To decode:
cat file | url64 -d
Bug-reports and pull-requests welcome. Everything is available under the MIT license (see LICENSE.MIT for details)