Kyle Beachill, a regular contributor to our forum, provided this nice class to authenticate using oAuth2.
================================================================================== '
'
' OAuth 2.0 Google Authenticator
' Developed by Kyle Beachill
' licence: MIT (http://www.opensource.org/licenses/mit-license.php)
'
' Inspired loosely by Tim Halls authentication classes in his Excel-Rest library:
' https://github.com/timhall/Excel-REST
'
'
' Features:
' Simple class to handle Google OAuth 2.0 Authentication
' Follows the Installed Application Flow
' Returns Simply the value for the Authorization header in API requests
'
' Gotchas:
' Tokens are held in plain text in the registry
'
' Required References:
' - Microsoft Internet Controls
' - Microsoft XML
'
' ================================================================================== '
Option Explicit
'// Simple enum for current authentication status
Private Enum AuthenticationStatus
NotAuthenticated = 1
TokenExpired = 2
Authenticated = 3
End Enum
'// Application Client ID and Application Secret
Private strClientId As String
Private strClientSecret As String
'// Authentication codes, tokens and expiry date
Private strTokenKey As String
Private strToken As String
Private strRefreshToken As String
Private dtExpiresWhen As Date
Private strAuthCode As String
'// Url End points for the authentication
Private strAuthUrl As String
Private strTokenUrl As String
Private strRedirectUri As String
'// Internet Explorer variables for initial authentication request
Private WithEvents oIExplorer As InternetExplorer
Private blnIeComplete As Boolean
Private strResponseText As String
Private oResponse As Object
'// Save the request object to prevent being created for each token expiry
Private objXMLRequest As MSXML2.ServerXMLHTTP
'// Since we are persisting the credentials to the registry, we need to read these in each time the class
'// is initialized, if they aren't found - these will be default values, "" for strings and 1900/01/01 for te date
Private Sub Class_Initialize()
Dim sDate As String
strToken = GetSetting("GoogleAuth", "Tokens", "Token")
strRefreshToken = GetSetting("GoogleAuth", "Tokens", "RefreshKey")
sDate = GetSetting("GoogleAuth", "Tokens", "TokenExpiry")
If Len(sDate) > 0 Then
dtExpiresWhen = CDate(sDate)
Else
dtExpiresWhen = #1/1/1900#
End If
End Sub
'// Allows the overriding of the default google EndPoints - these are unlikely to change
Public Sub InitEndPoints( _
Optional ByVal AuthUrl As String = "https://accounts.google.com/o/oauth2/auth", _
Optional ByVal TokenUrl As String = "https://accounts.google.com/o/oauth2/token", _
Optional ByVal RedirectUri As String = "urn:ietf:wg:oauth:2.0:oob" _
)
strAuthUrl = AuthUrl
strTokenUrl = TokenUrl
strRedirectUri = RedirectUri
End Sub
'// Application ID and Secret will always need passing, since they are required for refresh calls
'// Though these *could* be persisted in the registry also
Public Sub InitClientCredentials(ByVal ClientId As String, ByVal ClientSecret As String)
strClientId = ClientId
strClientSecret = ClientSecret
End Sub
'// Simple function to return the authentication status of the currently held credentials
Private Function getAuthenticationStatus() As AuthenticationStatus
'// If the Refresh Token Length is 0 then the initial authentication hasn't occurred
If Len(strRefreshToken) = 0 Then
getAuthenticationStatus = NotAuthenticated
Exit Function
End If
'// If the refresh date is less than now (with a 10 second buffer) then the token has expired
If dtExpiresWhen < DateAdd("s", 10, Now()) Then
getAuthenticationStatus = TokenExpired
Exit Function
End If
'// Otherwise the token is valid
getAuthenticationStatus = Authenticated
End Function
Private Sub GetNewToken()
Set oIExplorer = New InternetExplorer
With oIExplorer
.Navigate CreateAuthRequest()
.AddressBar = False
.MenuBar = False
.Resizable = False
.Visible = True
End With
'// Wait for userInteraction
Do: DoEvents: Loop Until blnIeComplete
'// Do we have an Authentication Code?
If Len(strAuthCode) = 0 Then
Err.Raise vbObjectError + 2, _
Description:="User cancelled Authentication"
End If
'// Now Get a new Token
If objXMLRequest Is Nothing Then Set objXMLRequest = New MSXML2.ServerXMLHTTP
With objXMLRequest
.Open "POST", strTokenUrl, False
.setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
.send CreateTokenRequest()
If .Status <> 200 Then
'// Error getting OAuth2 token
Err.Raise vbObjectError + .Status, _
Description:="Failed to retrieve OAuth2 Token - " & .Status & ": " & .responseText
End If
'// Get the credentials from the response
strToken = GetProp("access_token", .responseText)
strRefreshToken = GetProp("refresh_token")
dtExpiresWhen = DateAdd("s", CLng(GetProp("expires_in")), Now())
End With
'// Persist the Refresh key and expiry - the above should only ever need running once per application
SaveSetting "GoogleAuth", "Tokens", "RefreshKey", strRefreshToken
SaveSetting "GoogleAuth", "Tokens", "Token", strToken
SaveSetting "GoogleAuth", "Tokens", "TokenExpiry", CStr(dtExpiresWhen)
End Sub
Private Sub RefreshToken()
If objXMLRequest Is Nothing Then Set objXMLRequest = New MSXML2.ServerXMLHTTP
With objXMLRequest
.Open "POST", strTokenUrl, False
.setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
.send CreateRefreshRequest()
If .Status <> 200 Then
'// Error getting OAuth2 token
Err.Raise vbObjectError + .Status, _
Description:="Failed to retrieve OAuth2 Token - " & .Status & ": " & .responseText
End If
'// Get the credentials from the response
strToken = GetProp("access_token", .responseText)
dtExpiresWhen = DateAdd("s", CLng(GetProp("expires_in")), Now())
End With
'// Persist new token in registry
SaveSetting "GoogleAuth", "Tokens", "Token", strToken
SaveSetting "GoogleAuth", "Tokens", "TokenExpiry", CStr(dtExpiresWhen)
End Sub
'// Simple function that gets a propery from a single depth JSON formatted string
'// Requires the property name
'// Requires te JSON string on the first pass
Private Function GetProp(strPropName As String, Optional strJSObject As String = "") As String
Static oScriptControl As Object
If oScriptControl Is Nothing Then Set oScriptControl = CreateObject("ScriptControl")
With oScriptControl
.Language = "JScript"
.AddCode "function getProp(json, prop) { return json[prop]; }"
If Len(strJSObject) > 0 Then
strResponseText = strJSObject
Set oResponse = .eval("(" & strJSObject & ")")
End If
GetProp = .Run("getProp", oResponse, strPropName)
End With
End Function
'// Public property to return the Authorisation value header for a request
Public Property Get AuthHeader() As String
Dim eAuthStatus As AuthenticationStatus
eAuthStatus = getAuthenticationStatus
If eAuthStatus = NotAuthenticated Then
GetNewToken
ElseIf eAuthStatus = TokenExpired Then
RefreshToken
End If
AuthHeader = "Bearer " & strToken
End Property
'//===========================================================================================================
'// String building functions for the requests
'// Step 1: The initial url for authentication - Note the scope attribute, this sets what the application can access
Private Function CreateAuthRequest() As String
' Generate initial Authentication Request
' Using installed application flow: https://developers.google.com/accounts/docs/OAuth2InstalledApp
CreateAuthRequest = strAuthUrl
If InStr(1, CreateAuthRequest, "?") < 1 Then: CreateAuthRequest = CreateAuthRequest & "?"
CreateAuthRequest = CreateAuthRequest & "response_type=code"
CreateAuthRequest = CreateAuthRequest & "&client_id=" & strClientId
CreateAuthRequest = CreateAuthRequest & "&redirect_uri=" & strRedirectUri
CreateAuthRequest = CreateAuthRequest & "&scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fanalytics.readonly"
End Function
'// Step 2: The initial POST body to get the initial Token and refresh token
Private Function CreateTokenRequest() As String
CreateTokenRequest = "code=" & strAuthCode
CreateTokenRequest = CreateTokenRequest & "&client_id=" & strClientId
CreateTokenRequest = CreateTokenRequest & "&client_secret=" & strClientSecret
CreateTokenRequest = CreateTokenRequest & "&redirect_uri=" & strRedirectUri
CreateTokenRequest = CreateTokenRequest & "&grant_type=authorization_code"
End Function
'// Step 3: The POST body to refresh a token after it has expired
Private Function CreateRefreshRequest() As String
CreateRefreshRequest = "client_id=" & strClientId
CreateRefreshRequest = CreateRefreshRequest & "&client_secret=" & strClientSecret
CreateRefreshRequest = CreateRefreshRequest & "&refresh_token=" & strRefreshToken
CreateRefreshRequest = CreateRefreshRequest & "&grant_type=refresh_token"
End Function
'//===========================================================================================================
'// Event handling for Internet Explorer Object
'// OAuth 2.0 Process flow requires a user to provide access through the browser for initial Authentication
'//Break Loop on user Quit of IE
Private Sub oIExplorer_OnQuit()
blnIeComplete = True
End Sub
'//Check the title Window, if Success or Denied Found End the IE interaction
Private Sub oIExplorer_TitleChange(ByVal Text As String)
If InStr(1, Text, "Success") > 0 Then
strAuthCode = oIExplorer.Document.getElementbyid("code").Value
oIExplorer.Quit
ElseIf InStr(1, Text, "Denied") > 0 Then
oIExplorer.Quit
End If
End Sub
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