Google is happy to make sure you spend an hour figuring out why your base64 encoding is not working correctly

gistfile1.clj

;; From their doc at https://developers.google.com/accounts/docs/OAuth2ServiceAccount#authorizingrequests
;; You have to base64 a few parts of the request, including a so called "claim set"
;; This is what they claim to encode:
(def expected-claim "{\"iss\":\"761326798069-r5mljlln1rd4lrbhg75efgigp36m78j5@developer.gserviceaccount.com\",\"scope\":\"https://www.googleapis.com/auth/prediction\",\"aud\":\"https://www.googleapis.com/oauth2/v3/token\",\"exp\":1328554385,\"iat\":1328550785}")
;; And this is what they put as "base64" encoded string:
(def expected-encoded "eyJpc3MiOiI3NjEzMjY3OTgwNjktcjVtbGpsbG4xcmQ0bHJiaGc3NWVmZ2lncDM2bTc4ajVAZGV2ZWxvcGVyLmdzZXJ2aWNlYWNjb3VudC5jb20iLCJzY29wZSI6Imh0dHBzOi8vd3d3Lmdvb2dsZWFwaXMuY29tL2F1dGgvcHJlZGljdGlvbiIsImF1ZCI6Imh0dHBzOi8vYWNjb3VudHMuZ29vZ2xlLmNvbS9vL29hdXRoMi90b2tlbiIsImV4cCI6MTMyODU1NDM4NSwiaWF0IjoxMzI4NTUwNzg1fQ")
;; Well, decode it and you get 
(println (base64/decode expected-encoded))
;; "{\"iss\":\"761326798069-r5mljlln1rd4lrbhg75efgigp36m78j5@developer.gserviceaccount.com\",\"scope\":\"https://www.googleapis.com/auth/prediction\",\"aud\":\"https://accounts.google.com/o/oauth2/token\",\"exp\":1328554385,\"iat\":1328550785}"
;; Note that "aud" key and the associated URL. FFS.