Azure rsaKey from KeyVaultKeyResolver is always null

Question

I am saving identity documents via my MVC/Durandal web app to Azure blob storage. I am following this example to encrypt blobs in Azure storage using Azure key vault to store the encryption secret.

Here is my code:

    public async Task UploadIdentityDocumentForClient(string fileName, ParsedClientModel parsedClientModel)
    {
        BlobRequestOptions options = await GetBlobRequestOptions();
        await
            _storageRepository.CreateEncryptedBlobFromByteArray(_storageManager, _containerName, fileName, parsedClientModel.IdentityDocumentFile, parsedClientModel.IdentityDocumentContentType, options);
        return fileName;
    }


    private static async Task GetBlobRequestOptions()
    {
        string secretUri = WebConfigurationManager.AppSettings["SecretUri"];
        string secretName = WebConfigurationManager.AppSettings["SecretEncryptionName"];
    *1  KeyVaultKeyResolver keyVaultKeyResolver = new KeyVaultKeyResolver(GetAccessToken);

    *2  IKey rsaKey = keyVaultKeyResolver.ResolveKeyAsync($"{secretUri}/secrets/{secretName}", CancellationToken.None).GetAwaiter().GetResult();
        BlobEncryptionPolicy policy = new BlobEncryptionPolicy(rsaKey, null);
        BlobRequestOptions options = new BlobRequestOptions
        {
            EncryptionPolicy = policy
        };
        return options;
    }


     public static async Task GetAccessToken(string authority, string resource, string scope)
    {
        string clientId = WebConfigurationManager.AppSettings["ClientId"];
        string clientSecret = WebConfigurationManager.AppSettings["ClientSecret"];
        ClientCredential clientCredential = new ClientCredential(clientId, clientSecret);
        AuthenticationContext authenticationContext = new AuthenticationContext(authority, TokenCache.DefaultShared);
        AuthenticationResult result = await authenticationContext.AcquireTokenAsync(resource, clientCredential);
        if (result == null)
        {
            throw new InvalidOperationException(
                "GetAccessToken - Failed to obtain the Active Directory token for application.");
        }
    *3  return result.AccessToken;
    }


    public async Task CreateEncryptedBlobFromByteArray(IStorageManager storageManager, string containerName, string fileName,
        byte[] byteArray, string contentType, BlobRequestOptions options)
    {
        CloudBlobContainer container = await CreateStorageContainerIfNotExists(storageManager, containerName);
        CloudBlockBlob blob = container.GetBlockBlobReference(fileName);
        blob.Properties.ContentType = contentType;
        await blob.UploadFromByteArrayAsync(byteArray, 0, byteArray.Length, AccessCondition.GenerateEmptyCondition(), options, new OperationContext());
    }

This line...

    IKey rsaKey = keyVaultKeyResolver.ResolveKeyAsync($"{secretUri}/secrets/{secretName}", CancellationToken.None).GetAwaiter().GetResult();

always returns null.

I have added breakpoints (*1 to *3) in the code above and have noticed that *2 always gets hit before *3. This means that the KeyVaultKeyResolver(GetAccessToken) call is not waiting for the GetAccessToken call to return with the value.

Any ideas as to what I am doing wrong?

Answer 1

I figured out what I was doing wrong.

Where breakpoint 2 is I should have used this code:

SymmetricKey sec = (SymmetricKey) cloudResolver
            .ResolveKeyAsync("https://yourkeyvault.vault.azure.net/secrets/MiplanAdminLocalEncryption",
                CancellationToken.None)
            .GetAwaiter()
            .GetResult();

I also had to add the secret to my Azure Key Vault using PowerShell. Creating the secret via the management UI did not work. Here are the commands I used:

Sorry for image but SO would not accept the above text even when pasted as a code sample.

See this site for the original example.

I found a way to add the secret via the Azure portal:

    //If entering via Azure UI:
    //Your secret string must be 16 characters (28 bits) long or end up being 28, 192, 256, 384, or 512 bits.
    // Base64 encode using https://www.base64encode.org/
    //Take this encoded value and enter it as the secret value in the UI.