(Tcl) Get Google Cloud Storage Access Token using Service Account JSON Private Key

Demonstrates how to get a Google Cloud Storage access token using a JSON service account private key. Obtaining an access token for a service account requires no user interaction (it does not require a browser, nor callback URI's, etc.).

When an access token expires, an application can be (and should be) designed to automatically fetch a new access token.

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load ./chilkat.dll

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

# First load the JSON key into a string.
set fac [new_CkFileAccess]

set jsonKey [CkFileAccess_readEntireTextFile $fac "qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json" "utf-8"]
if {[CkFileAccess_get_LastMethodSuccess $fac] != 1} then {
    puts [CkFileAccess_lastErrorText $fac]
    delete_CkFileAccess $fac
    exit
}

# A JSON private key should look something like this:

# 	{
# 	  "type": "service_account",
# 	  "project_id": "chilkattest-1350",
# 	  "private_key_id": "fa2e36ee26986eab628b59868af8bec1d1c64c38",
# 	  "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvgIjFa...28N64N2n1E4FYzBZjSdy\n-----END PRIVATE KEY-----\n",
# 	  "client_email": "598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a@developer.gserviceaccount.com",
# 	  "client_id": "598922945226-00rb0ppfg0snd9jo7bhvd4v17jtj2d3a.apps.googleusercontent.com",
# 	  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
# 	  "token_uri": "https://accounts.google.com/o/oauth2/token",
# 	  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
# 	  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a%40developer.gserviceaccount.com"
# 	}

set gAuth [new_CkAuthGoogle]

CkAuthGoogle_put_JsonKey $gAuth $jsonKey

# Choose a scope.
CkAuthGoogle_put_Scope $gAuth "https://www.googleapis.com/auth/cloud-platform"

# Request an access token that is valid for this many seconds.
CkAuthGoogle_put_ExpireNumSeconds $gAuth 3600

# If the application is requesting delegated access:
# The email address of the user for which the application is requesting delegated access,
# then set the email address here. (Otherwise leave it empty.)
CkAuthGoogle_put_SubEmailAddress $gAuth ""

# Connect to www.googleapis.com using TLS (TLS 1.2 is the default.)
# The Chilkat socket object is used so that the connection can be established
# through proxies or an SSH tunnel if desired.
set tlsSock [new_CkSocket]

set success [CkSocket_Connect $tlsSock "www.googleapis.com" 443 1 5000]
if {$success != 1} then {
    puts [CkSocket_lastErrorText $tlsSock]
    delete_CkFileAccess $fac
    delete_CkAuthGoogle $gAuth
    delete_CkSocket $tlsSock
    exit
}

# Send the request to obtain the access token.
set success [CkAuthGoogle_ObtainAccessToken $gAuth $tlsSock]
if {$success != 1} then {
    puts [CkAuthGoogle_lastErrorText $gAuth]
    delete_CkFileAccess $fac
    delete_CkAuthGoogle $gAuth
    delete_CkSocket $tlsSock
    exit
}

# Examine the access token:
puts "Access Token: [CkAuthGoogle_accessToken $gAuth]"

# We're going to save this access token to a file to be used
# by other examples.
set sbToken [new_CkStringBuilder]

CkStringBuilder_Append $sbToken [CkAuthGoogle_accessToken $gAuth]
CkStringBuilder_WriteFile $sbToken "qa_data/tokens/googleCloudStorageAccessToken.txt" "utf-8" 0

delete_CkFileAccess $fac
delete_CkAuthGoogle $gAuth
delete_CkSocket $tlsSock
delete_CkStringBuilder $sbToken