CosmosDB authentication with Managed Identities

Cosmos.cs

private static async Task<RestClient> GetRestClientAsync()
{
    var azureServiceTokenProvider = new AzureServiceTokenProvider();
    var accessToken = await azureServiceTokenProvider.GetAccessTokenAsync("https://management.azure.com/").ConfigureAwait(false);
    var restTokenCredentials = new Microsoft.Rest.TokenCredentials(accessToken);
    var azCred = new AzureCredentials(restTokenCredentials, null, tenantId, AzureEnvironment.AzureGlobalCloud);
    return RestClient.Configure().WithEnvironment(AzureEnvironment.AzureGlobalCloud).WithCredentials(azCred).Build();
}
        
static async Task CosmosDBTest()
{
    var cosmosDBManagementClient = new CosmosDBManagementClient(await GetRestClientAsync());
    cosmosDBManagementClient.SubscriptionId = subscriptionId;

    var cosmosResource = await cosmosDBManagementClient.DatabaseAccounts.GetWithHttpMessagesAsync(resourceGroupName,cosmosDBName);
    //If the managed Identity has more "power" you could do a ListKeysWithHttpMessagesAsync and retrieve the "write"key too
    var cosmosKeys = await cosmosDBManagementClient.DatabaseAccounts.ListReadOnlyKeysWithHttpMessagesAsync(resourceGroupName, cosmosDBName);
    Console.WriteLine($"Primary key for cosmos account: {cosmosKeys.Body.PrimaryReadonlyMasterKey}");

    var cosmosClient = new CosmosClient(cosmosResource.Body.DocumentEndpoint, cosmosKeys.Body.PrimaryReadonlyMasterKey );
    var createDBOperation = await cosmosClient.CreateDatabaseIfNotExistsAsync(dbname);
}

cosmos.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Azure.Services.AppAuthentication" Version="1.4.0" />
    <PackageReference Include="Microsoft.Rest.ClientRuntime" Version="3.0.3" />
    <PackageReference Include="Microsoft.Azure.Cosmos" Version="3.6.0" />
    <PackageReference Include="Microsoft.Azure.Management.Fluent" Version="1.31.0" />
    <PackageReference Include="Microsoft.Azure.Management.CosmosDB.Fluent" Version="1.31.0" />
  </ItemGroup>

</Project>