OPS.bas

Private pClient As WebClient
Public Property Get Client() As WebClient
    If pClient Is Nothing Then
        Set pClient = New WebClient
        pClient.BaseUrl = "https://ops.epo.org/3.1/"
        
        ' Setup authenticator (note: provide consumer key and secret here
        Dim Auth As New OPSAuthenticator
        Auth.Setup "CONSUMER_KEY", "CONSUMER_SECRET"
        
        ' If there are issues automatically getting the token with consumer key / secret
        ' the token can be found in the developer console and manually entered here
        ' Auth.Token = "AUTH_TOKEN"
        
        Set pClient.Authenticator = Auth
        
        ' Add XML converter
        WebHelpers.RegisterConverter "xml", "application/xml", "OPS.ConvertToXml", "OPS.ParseXml"
    End If
    
    Set Client = pClient
End Property

Public Function Search(Query As String) As WebResponse
    Dim Request As New WebRequest
    Request.Resource = "rest-services/published-data/search"
    Request.CustomResponseFormat = "xml"
    Request.AddQuerystringParam "q", Query
    
    Set Search = Client.Execute(Request)
End Function

' Enable XML parsing/converting
' https://github.com/VBA-tools/VBA-Web/wiki/XML-Support-in-4.0
Public Function ParseXml(Value As String) As Object
    Set ParseXml = CreateObject("MSXML2.DOMDocument")
    ParseXml.Async = False
    ParseXml.LoadXML Value
End Function

Public Function ConvertToXml(Value As Variant) As String
    ConvertToXml = VBA.Trim$(VBA.Replace(Value.Xml, vbCrLf, ""))
End Function

OPSAuthenticator.cls

''
' OPSAuthenticator v3.0.0
' (c) Tim Hall - https://github.com/VBA-tools/VBA-Web
'
' OAuth2 client credentials authenticator for OPS
'
' @class OPSAuthenticator
' @implements IWebAuthenticator v4.*
' @author [email protected]
' @license MIT
'' ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ '
Implements IWebAuthenticator
Option Explicit

Public ConsumerKey As String
Public ConsumerSecret As String

Public Token As String

' ============================================= '
' Public Methods
' ============================================= '

''
' Setup authenticator
''
Public Sub Setup(ConsumerKey As String, ConsumerSecret As String)
    Me.ConsumerKey = ConsumerKey
    Me.ConsumerSecret = ConsumerSecret
End Sub

''
' Hook for taking action before a request is executed
'
' @param {WebClient} Client The client that is about to execute the request
' @param in|out {WebRequest} Request The request about to be executed
''
Private Sub IWebAuthenticator_BeforeExecute(ByVal Client As WebClient, ByRef Request As WebRequest)
    If Me.Token = "" Then
        Me.Token = Me.GetToken(Client)
    End If
    
    Request.SetHeader "Authorization", "Bearer " & Me.Token
End Sub

''
' Hook for taking action after request has been executed
'
' @param {WebClient} Client The client that executed request
' @param {WebRequest} Request The request that was just executed
' @param in|out {WebResponse} Response to request
''
Private Sub IWebAuthenticator_AfterExecute(ByVal Client As WebClient, ByVal Request As WebRequest, ByRef Response As WebResponse)
    ' e.g. Handle 401 Unauthorized or other issues
End Sub

''
' Hook for updating http before send
'
' @param {WebClient} Client
' @param {WebRequest} Request
' @param in|out {WinHttpRequest} Http
''
Private Sub IWebAuthenticator_PrepareHttp(ByVal Client As WebClient, ByVal Request As WebRequest, ByRef Http As Object)
    ' e.g. Update option, headers, etc.
End Sub

''
' Hook for updating cURL before send
'
' @param {WebClient} Client
' @param {WebRequest} Request
' @param in|out {String} Curl
''
Private Sub IWebAuthenticator_PrepareCurl(ByVal Client As WebClient, ByVal Request As WebRequest, ByRef Curl As String)
    ' e.g. Add flags to cURL
End Sub

Public Function GetToken(Client As WebClient) As String
    Dim TokenClient As WebClient
    Dim TokenRequest As New WebRequest
    Dim Encoded As String
    Dim TokenResponse As WebResponse
    
    ' Clone client to avoid accidental interactions
    Set TokenClient = Client.Clone
    Set TokenClient.Authenticator = Nothing
    
    ' Setup request according to docs
    ' http://documents.epo.org/projects/babylon/eponet.nsf/0/7AF8F1D2B36F3056C1257C04002E0AD6/$File/OPS_v3.1_documentation_version_1.2.14_en.pdf
    TokenRequest.Resource = "auth/accesstoken"
    TokenRequest.RequestFormat = WebFormat.FormUrlEncoded
    TokenRequest.ResponseFormat = WebFormat.Json
    TokenRequest.Method = WebMethod.HttpPost
    
    ' Add encoded consumer key/secret as basic authentication
    Encoded = WebHelpers.Base64Encode(Me.ConsumerKey & ":" & Me.ConsumerSecret)
    TokenRequest.SetHeader "Authorization", "Basic " & Encoded
    
    ' Set grant_type in body
    TokenRequest.AddBodyParameter "grant_type", "client_credentials"
    
    Set TokenResponse = TokenClient.Execute(TokenRequest)
    If TokenResponse.StatusCode = WebStatusCode.Ok Then
        GetToken = TokenResponse.Data("access_token")
    Else
        WebHelpers.LogError "Failed to load token, " & TokenResponse.StatusCode & ": " & TokenResponse.Content
    End If
End Function

Testing.bas

Sub Test()
    WebHelpers.EnableLogging = True
    
    Dim Response As WebResponse
    Set Response = OPS.Search("plastic")
    If Response.StatusCode <> WebStatusCode.Ok Then
        Exit Sub
    End If
    
    Debug.Print "Search Results"
    Debug.Print "--------------"
    
    Dim Result As Variant
    Dim Family As String
    Dim DocumentNumber As String
    
    ' world-patent-data > biblio-search > search-result > [publication-reference...]
    For Each Result In Response.Data.LastChild.LastChild.LastChild.ChildNodes
        Family = Result.Attributes(1).NodeValue
        DocumentNumber = Result.FirstChild.ChildNodes(1).Text
        
        Debug.Print "Result - " & Family & ", " & DocumentNumber
    Next Result
End Sub