From 61f101ebca8b351bc46619cfd0e67e8639111b48 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bl=C3=B6cher=20Johanna=20Ruth?= <bloecher@fzp.czu.cz>
Date: Wed, 24 Jun 2020 15:39:30 +0200
Subject: [PATCH] Added code challenger and code verification to ee
 authorisation routine.

---
 R/auth.R                                 |  8 ++++----
 inst/Python/ee_authorisation_function.py | 26 ++++++++++++++++++++----
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/R/auth.R b/R/auth.R
index 35eb1a6..82f02d3 100755
--- a/R/auth.R
+++ b/R/auth.R
@@ -35,20 +35,20 @@ run_ee_oauth <- function() {
     load_test <- try(source_python(file = oauth_func_path), silent = T)
     count <- count + 1
   }
-  request_ee_code()
+  verify <- request_ee_code()
   
   code <-
     readline("Enter authorisation code for Earth Engine API here: ")
   
-  test <- try(request_ee_token(code), silent = T)
+  test <- try(request_ee_token(code, verify), silent = T)
   
   while (class(test) == "try-error") {
     cat(
       "Problem with Authentication key input. \nPlease follow the authentication steps in the browser and copy paste the authentication token into the R console again."
     )
-    request_ee_code()
+    verify <- request_ee_code()
     code <- readline("enter authorisation code here: ")
-    test <- try(request_ee_token(code), silent = T)
+    test <- try(request_ee_token(code, verify), silent = T)
   }
   cat("Earth Engine Python API is authenticated \n")
 }
diff --git a/inst/Python/ee_authorisation_function.py b/inst/Python/ee_authorisation_function.py
index 53953da..bb8d336 100755
--- a/inst/Python/ee_authorisation_function.py
+++ b/inst/Python/ee_authorisation_function.py
@@ -4,20 +4,38 @@
 import urllib
 from ee.oauth import get_credentials_path
 import json
+import os
+import base64
+import hashlib
 
 ft_scope = 'https://www.googleapis.com/auth/fusiontables'
 
 
 def request_ee_code():
-    # get authorisation url
-    auth_url = ee.oauth.get_authorization_url()
+    out = create_codes()
+    code_verifier = out[0]
+    code_challenge = out[1]
+     # get authorisation url
+    auth_url = ee.oauth.get_authorization_url(code_challenge)
     # call auth_url in browser to grand access by the user
     webbrowser.open_new(auth_url)
+    return code_verifier
 
-def request_ee_token(auth_code):
-    token = ee.oauth.request_token(auth_code)
+def request_ee_token(auth_code, code_verifier):
+    token = ee.oauth.request_token(auth_code, code_verifier)
     ee.oauth.write_token(token)
 
+    
+def _base64param(byte_string):
+  """Encodes bytes for use as a URL parameter."""
+  return base64.urlsafe_b64encode(byte_string).rstrip(b'=')
+  
+def create_codes():
+  code_verifier = _base64param(os.urandom(32))
+  code_challenge = _base64param(hashlib.sha256(code_verifier).digest())
+  return code_verifier, code_challenge
+
+