How use AddMicrosoftIdentityWebApiAuthentication without appsettings section?

I am implementing an Azure Active Directory in a .NET 5 API. I currently have this API perfectly running on .NET Core 2.2.

This is the old working code:

services.AddAuthentication(AzureADDefaults.BearerAuthenticationScheme)
    .AddAzureADBearer(options =>
    {
         options.Instance = "https://login.microsoftonline.com/";
         options.Domain = backOfficeADDomain;
         options.TenantId = backOfficeADTenantId;
         options.ClientId = $"api://{backOfficeADAPIClientId}";
         options.ClientSecret = backOfficeADAPISecret;
    });

But since the update to .NET 5 I get this warning:

'AzureADAuthenticationBuilderExtensions.AddAzureADBearer(AuthenticationBuilder, Action)' is obsolete: 'This is obsolete and will be removed in a future version. Use AddMicrosoftWebApiAuthentication from Microsoft.Identity.Web instead. See https://aka.ms/ms-identity-web.'

So I tried updating it to this:

services.AddMicrosoftIdentityWebApiAuthentication(_configuration, "AzureAd");

It seems that an "AzureAd" section in the appsettings.json is the only way to pass the credentials. How can I manually enter the Instance, domain, ClientId, etc..? I don't use the appsettings.json, all the data is manually retrieved from AzureKeyVault.

Thank you!

IConfigurationSection azureAdSection = _configuration.GetSection("AzureAd");

azureAdSection.GetSection("Instance").Value = "https://login.microsoftonline.com/";
azureAdSection.GetSection("Domain").Value = backOfficeADDomain;
azureAdSection.GetSection("TenantId").Value = backOfficeADTenantId;
azureAdSection.GetSection("ClientId").Value = backOfficeADAPIClientId;
azureAdSection.GetSection("ClientSecret").Value = backOfficeADAPISecret;

services.AddMicrosoftIdentityWebApiAuthentication(_configuration, "AzureAd");