OAuth Generator

#filepath to store credentials
my_creds=~/oauth_cache.txt

client_id=''
client_secret=''
redirectURI=''

if [ -s $my_creds ]; then
  # if we already have a token stored, use it
  . $my_creds
  time_now=`date +%s`
else
  scope='https://www.googleapis.com/auth/analytics'
  # Form the request URL
  # http://goo.gl/U0uKEb
  auth_url="https://accounts.google.com/o/oauth2/auth?client_id=$client_id&scope=$scope&response_type=code&redirect_uri=$redirectURI"

  echo "Please go to:"
  echo
  echo "$auth_url"
  echo
  echo "after accepting, enter the code you are given:"
  read auth_code

  # swap authorization code for access and refresh tokens
  # http://goo.gl/Mu9E5J
  auth_result=$(curl -s https://accounts.google.com/o/oauth2/token \
    -H "Content-Type: application/x-www-form-urlencoded" \
    -d code=$auth_code \
    -d client_id=$client_id \
    -d client_secret=$client_secret \
    -d redirect_uri=urn:ietf:wg:oauth:2.0:oob \
    -d grant_type=authorization_code)
  access_token=$(echo -e "$auth_result" | \
                 ggrep -Po '"access_token" *: *.*?[^\\]",' | \
                 awk -F'"' '{ print $4 }')
  refresh_token=$(echo -e "$auth_result" | \
                  ggrep -Po '"refresh_token" *: *.*?[^\\]",*' | \
                  awk -F'"' '{ print $4 }')
  expires_in=$(echo -e "$auth_result" | \
               ggrep -Po '"expires_in" *: *.*' | \
               awk -F' ' '{ print $3 }' | awk -F',' '{ print $1}')
  time_now=`date +%s`
  expires_at=$((time_now + expires_in - 60))
  echo -e "access_token=$access_token\nrefresh_token=$refresh_token\nexpires_at=$expires_at" > $my_creds
  echo -e "\n#Static data\nclientID=$client_id\nclientSecret=$client_secret\nredirectURI=$redirectURI" >> $my_creds
fi

# if our access token is expired, use the refresh token to get a new one
# http://goo.gl/71rN6V
if [ $time_now -gt $expires_at ]; then
  refresh_result=$(curl -s https://accounts.google.com/o/oauth2/token \
   -H "Content-Type: application/x-www-form-urlencoded" \
   -d refresh_token=$refresh_token \
   -d client_id=$client_id \
   -d client_secret=$client_secret \
   -d grant_type=refresh_token)
  access_token=$(echo -e "$refresh_result" | \
                 ggrep -Po '"access_token" *: *.*?[^\\]",' | \
                 awk -F'"' '{ print $4 }')
  expires_in=$(echo -e "$refresh_result" | \
               ggrep -Po '"expires_in" *: *.*' | \
               awk -F' ' '{ print $3 }' | awk -F',' '{ print $1 }')
  time_now=`date +%s`
  expires_at=$(($time_now + $expires_in - 60))
  echo -e "access_token=$access_token\nrefresh_token=$refresh_token\nexpires_at=$expires_at" > $my_creds
  echo -e "\n#Static data\nclientID=$client_id\nclientSecret=$client_secret\nredirectURI=$redirectURI" >> $my_creds
fi