There could be multiple ways to access the keys from Key Vault in a .NET Core application, but you could choose from the 2 explained below.
To access key vault secrets using C# SDK, you will have to install the below NuGet packages:
Now, there is some code that you have to write to initialize the Key Vault SDK object. But the main thing here is how your app will be considered as an authenticated app that could use or access Azure Key Vault.
Here comes, DefaultAzureCredential object. This is the main object, that helps your .NET Core application to get an Azure Identity (could be either Service Principal, Managed Identity, or a User Identity). And this identity is further used to check whether it has permission to access Key Vault or not.
So, now there are again 3 ways you can go ahead with:
For azure hosted apps, I would recommend going with Managed Identity as you don't have to manage any client id and secrets in your application. DefaultAzureCredential will automatically pick the Managed Identity from Azure App Service or Function App.
For azure hosted & local development, we can create a Service Principal, and keep the following variables in the environment variable. One way to put keys in Environment Variable is to put them in localsettings.json.
For local development only, as Managed Identity does not work locally. So, another way to access Key Vault from the development environment is to go to Visual Studio > Tools > Options > Azure Service Authentication. Log in with a user from your Azure AD account. DefaultAzureCredential will pick this value if it fails to get identity from Environment Variable and Managed Identity.
DefaultAzureCredential looks in the below order to get the Azure Credentials.