ClearBank.NET

Unofficial .NET client for ClearBank integration, creating online payments via their API. Bank payment handling automation in the United Kingdom. Released as a NuGet package. This aims to be bare and easy.

Here are the pre-conditions:

1. Create Azure KeyVault

From the Access Policies, add the role, and "Key Permissions" for the Sign & Verify. Azure KeyVault supports HSM (hardware security module) backed keys.

2. Configure the Certificate -tab

For example, use a new self-signed certificate, but the PEM format has to be selected.

Download the certificate, a PEM-file.

3. Create a CSR with Open-SSL and upload it to the ClearBank portal

openssl.exe req -new -sha256 -key "c:\temp\downloaded.pem" -out file.csr

• Upload that to the portal https://institution-sim.clearbank.co.uk/
• Copy the private key (the long string) from the message box. You need that in the config later, as that will be used in the POST header Authorization: Bearer (the long string)

Update: You can also get CSR now directly from Azure keyvault, by selecting the certificate and clicking "Certificate Operation" -> "Download CSR"

(4. Optional: Ensure the correctness with FI-API-Signtool)

The signing is done similarly than in this repo, but the official code is more messy as it's C#. GitHub - clearbank/fi-api-signtool

5. Start using this library

Your user code should look something like this:

let doSomeTransactions =
    let clearbankDefaultConfig =
        {
            BaseUrl = "https://institution-api-sim.clearbank.co.uk/"
            PrivateKey = "..."
            AzureKeyVaultName =  "myVault"
            AzureKeyVaultCredentials = DefaultCredentials
        } : ClearbankConfigruation

    let azureKeyVaultCertificateName = "my-cert"
    let fromAccount = UK_Domestic("60-01-34", "51112345")

    let target1 = 
        {
            To = UK_Domestic("20-20-15", "55555555")
            AccountHolder = "Mr Test"
            Sum = 123.00m
            Currency = "GBP"
            Description = "Phone Bill"
            PaymentReference = "123456789"
            TransactionId = "12345" // End-to-end: You identify corresponding webhooks with this.
        } |> ClearBank.createCreditTransfer

    let target2 = 
        {
            To = UK_Domestic("40-47-84", "70872490")
            AccountHolder = "John Doe"
            Sum = 123.00m
            Currency = "GBP"
            Description = "Some money"
            PaymentReference = "12345"
            TransactionId = "12345"
        } |> ClearBank.createCreditTransfer

    let xReqId = Guid.NewGuid()
    let instructions = ClearBank.createPaymentInstruction "Batch123" fromAccount  [| target1 ; target2 |]
    ClearBank.transferPayments clearbankDefaultConfig azureKeyVaultCertificateName xReqId [| instructions |] |> Async.RunSynchronously

If you have problems with the KeyVault authentication, you can change the AzureKeyVaultCredentials in the config

    let clearbankDefaultConfig =
        {
            BaseUrl = "https://institution-api-sim.clearbank.co.uk/"
            PrivateKey = "..."
            AzureKeyVaultName =  "..."
            AzureKeyVaultCertificateName = "..."
            AzureKeyVaultCredentials =
                CredentialsWithOptions (
                    Azure.Identity.DefaultAzureCredentialOptions (
                        //ExcludeEnvironmentCredential = true
                        //,ExcludeManagedIdentityCredential = true
                        ExcludeSharedTokenCacheCredential = true
                        ,ExcludeVisualStudioCredential = true
                        //,ExcludeVisualStudioCodeCredential = true
                        //,ExcludeAzureCliCredential = true
                        //,ExcludeInteractiveBrowserCredential = true
                    )) 
            LogUnsuccessfulHandler = None
        } : ClearbankConfiguration

The last LogUnsuccessfulHandler property is an optional error-logging callback. You could replace it e.g. with Some logging and have a function:

    let logging(status,content) =
        match ClearBank.parseClarBankErrorContent content with
        | ClearBankEmptyResponse -> Console.WriteLine "Response was empty"
        | ClearBankTransactionError errors -> errors |> Seq.iter(fun (tid,err) -> Console.WriteLine("Transaction id " + tid + " failed for " + err))
        | ClearBankGeneralError(title, detail) -> Console.WriteLine(title + ", " + detail)
        | ClearBankUnknownError content -> Console.WriteLine("JSON: " + content)

Creating accounts

There is a method ClearBank.createNewAccount to create new accounts.

Getting accounts and transactions

There are methods ClearBank.getAccounts, that you can use for e.g. getting balances, and ClearBank.getTransactions config pageSize pageNumber startDate endDate

Webhook responses

To receive webhooks, you need a web server, which is outside the scope of this library. However, there are some helper classes provided in this library.

To use those, your server code could look something like this:

type CBWebhookController() as this =
    inherit ApiController()

    member __.Post ()
        async {
            // 1. Verify the webhook against your ClearBank public key:

            // Download the public key (a .pem file) from your ClearBank portal and use a converter such as https://raskeyconverter.azurewebsites.net/PemToXml to convert the text to XML
            let publicKeyXml = "<RSAKeyValue>...</RSAKeyValue>"

            let signature = this.Request.Headers.GetValues("DigitalSignature") |> Seq.tryHead |> Option.map Convert.FromBase64String //add some error handling
            let! bodyJson = this.Request.Content.ReadAsStringAsync() |> Async.AwaitTask

            let! isVerified = ClearBank.verifySignature publicKeyXml signature bodyJson //proceed only if true

            // 2. Parse and handle the request:
            let parsed = ClearBankWebhooks.parsePaymentsCall bodyJson

            // Use parsed.Type to get the webhook type.
            // Different types may have the corresponding end-to-end transactionId in different places.
            // Fetch your transaction based on that ID, and do whatever you want.

            //    match parsed.Type with
            //    | "TransactionSettled" -> ...
            //    | "PaymentMessageAssessmentFailed" -> ...
            //    | "PaymentMessageValidationFailed" -> ...
            //    | "TransactionRejected" -> ...
            //    | _ -> (* "FITestEvent" *) ...

            // 3. Create response
            return! ClearBankWebhooks.createResponse clearbankDefaultConfig azureKeyVaultCertificateName this.Request parsed.Nonce

        } |> Async.StartAsTask

To test webhooks, you can use e.g. Fiddler to compose them and https://webhook.site/ to get their calls.