(PureBasic) OAuth2 for a GMail using a JSON Service Account Key

Demonstrates how get an OAuth2 access token for GMail (Google Service Account) using a JSON private key.

After the access token is obtained, it may be used to send email. When the access token expires, a new access token needs to be obtained (using this same procedure).

Note: This is for OAuth2 using Google Service account keys.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkSocket.pb"
IncludeFile "CkAuthGoogle.pb"
IncludeFile "CkEmail.pb"
IncludeFile "CkFileAccess.pb"
IncludeFile "CkMailMan.pb"

Procedure ChilkatExample()

    ; 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.
    fac.i = CkFileAccess::ckCreate()
    If fac.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    jsonKey.s = CkFileAccess::ckReadEntireTextFile(fac,"qa_data/googleApi/ChilkatTest-ab2ecd52ef98.json","utf-8")
    If CkFileAccess::ckLastMethodSuccess(fac) <> 1
        Debug CkFileAccess::ckLastErrorText(fac)
        CkFileAccess::ckDispose(fac)
        ProcedureReturn
    EndIf

    ; A JSON private key should look 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"
    ; 	}

    gAuth.i = CkAuthGoogle::ckCreate()
    If gAuth.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkAuthGoogle::setCkJsonKey(gAuth, jsonKey)

    ; Choose a scope.
    CkAuthGoogle::setCkScope(gAuth, "https://mail.google.com/")

    ; Request an access token that is valid for this many seconds.
    CkAuthGoogle::setCkExpireNumSeconds(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::setCkSubEmailAddress(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.
    tlsSock.i = CkSocket::ckCreate()
    If tlsSock.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkSocket::ckConnect(tlsSock,"www.googleapis.com",443,1,5000)
    If success <> 1
        Debug CkSocket::ckLastErrorText(tlsSock)
        CkFileAccess::ckDispose(fac)
        CkAuthGoogle::ckDispose(gAuth)
        CkSocket::ckDispose(tlsSock)
        ProcedureReturn
    EndIf

    ; Send the request to obtain the access token.
    success = CkAuthGoogle::ckObtainAccessToken(gAuth,tlsSock)
    If success <> 1
        Debug CkAuthGoogle::ckLastErrorText(gAuth)
        CkFileAccess::ckDispose(fac)
        CkAuthGoogle::ckDispose(gAuth)
        CkSocket::ckDispose(tlsSock)
        ProcedureReturn
    EndIf

    ; Examine the access token:
    Debug "Access Token: " + CkAuthGoogle::ckAccessToken(gAuth)

    ; Now that we have the access token, it may be used to send email
    ; while it remains valid.  Once the access token expires, a new access token 
    ; should be obtained using the same code as above.

    ; -----------------------------------------------------------------------
    mailman.i = CkMailMan::ckCreate()
    If mailman.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Set the properties for the GMail SMTP server:
    CkMailMan::setCkSmtpHost(mailman, "smtp.gmail.com")
    CkMailMan::setCkSmtpPort(mailman, 587)
    CkMailMan::setCkStartTLS(mailman, 1)

    CkMailMan::setCkSmtpUsername(mailman, "YOUR_GOOGLE_APPS_USER_EMAIL_ADDRESS")
    CkMailMan::setCkOAuth2AccessToken(mailman, CkAuthGoogle::ckAccessToken(gAuth))

    ; Create a new email object
    email.i = CkEmail::ckCreate()
    If email.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkEmail::setCkSubject(email, "This is a test")
    CkEmail::setCkBody(email, "This is a test")
    CkEmail::setCkFrom(email, "YOUR NAME <YOUR_GOOGLE_APPS_USER_EMAIL_ADDRESS>")
    success = CkEmail::ckAddTo(email,"Chilkat Admin","admin@chilkatsoft.com")
    ; To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

    ; Call SendEmail to connect to the SMTP server and send.
    ; The connection (i.e. session) to the SMTP server remains
    ; open so that subsequent SendEmail calls may use the
    ; same connection.  
    success = CkMailMan::ckSendEmail(mailman,email)
    If success <> 1
        Debug CkMailMan::ckLastErrorText(mailman)
        CkFileAccess::ckDispose(fac)
        CkAuthGoogle::ckDispose(gAuth)
        CkSocket::ckDispose(tlsSock)
        CkMailMan::ckDispose(mailman)
        CkEmail::ckDispose(email)
        ProcedureReturn
    EndIf

    ; You may close the connection here.  If the connection is kept open, 
    ; the next call to mailman.SendEmail will continue using the already-established connection
    ; (and automatically re-connect if needed).
    success = CkMailMan::ckCloseSmtpConnection(mailman)
    If success <> 1
        Debug "Connection to SMTP server not closed cleanly."
    EndIf

    Debug "Email Sent via GMail using an OAuth2 Service Account Key."


    CkFileAccess::ckDispose(fac)
    CkAuthGoogle::ckDispose(gAuth)
    CkSocket::ckDispose(tlsSock)
    CkMailMan::ckDispose(mailman)
    CkEmail::ckDispose(email)


    ProcedureReturn
EndProcedure