Google OAuth 2.0 Walkthrough Script - script to help step through getting an access token for Google API calls (w/o needing a domain/server)

GoogleOauthWalkthrough.sh

#!/bin/bash

# Variables
client_id=""
client_secret=""

scopes=""
auth_code=""

access_token=""
refresh_token=""

#### Usage ####
## Set whichever variables above that you have so far, leave the rest blank (none is fine).
## The script will print instructions on what to do next based on what you have.
## If enough variables are set, the access_token and refresh_token will be retrieved.
## If access_token is set, it will be validated.
## If refresh_token is set and access_token validation fails, a refresh will be attempted.
###############

# 1) Client/Project Creds
if [[ -z $client_id || -z $client_secret ]]; then
    echo 'https://console.developers.google.com/';
    echo 'Go to the above URL and register a project w/ relevant APIs...'
    echo '...then create an Oauth Consent Screen w/ the appropriate scopes and test users...'
    echo '...then create an OAuth Client for a Desktop Application to get the client id and secret.'
    exit 1
fi

# 2) OAuth2 Auth Code
if [[ -z $auth_code ]]; then
    echo "Go to this URL to complete the OAuth flow to get the auth code: "
    echo "https://accounts.google.com/o/oauth2/auth?client_id=$client_id&redirect_uri=urn:ietf:wg:oauth:2.0:oob&response_type=code&scope=$scopes"
    exit 2
fi

# 3) OAuth2 Tokens
if [[ -z $access_token && -z $refresh_token ]]; then
    echo "Attempting to get tokens..."
    _tokenData="client_id=$client_id&client_secret=$client_secret&code=$auth_code&redirect_uri=urn:ietf:wg:oauth:2.0:oob&grant_type=authorization_code"
    curl --request POST --data $_tokenData "https://accounts.google.com/o/oauth2/token"
    exit 0
fi

# 4) Validate Token
if [[ -n $access_token ]]; then
    echo "Attempting token validation..."
    if curl -f "https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=$access_token"; then
        echo "Validated Access Token: $access_token"
        exit 0
    fi
fi

#5) Refresh Tokens
if [[ -n $refresh_token ]]; then
    echo "Attempting token refresh..."
    _refreshData="client_id=$client_id&client_secret=$client_secret&refresh_token=$refresh_token&grant_type=refresh_token"
    curl --request POST --data $_refreshData "https://accounts.google.com/o/oauth2/token"
else
    echo "Refresh attempt skipped, no refresh_token set."
    exit 3
fi