managed-identity-based-authentication.yml

### YamlMime:HowTo

---
metadata:
  title: Use system-assigned managed identities to access Azure Cosmos DB data
  description: Learn how to configure a Microsoft Entra system-assigned managed identity (managed service identity) to access keys from Azure Cosmos DB.
  author: seesharprun
  ms.author: sidandrews
  ms.reviewer: justipat
  ms.date: 06/25/2024
  ms.service: cosmos-db
  ms.subservice: nosql
  ms.topic: how-to
  ms.custom:
    - devx-track-csharp
    - devx-track-azurecli
    - subject-rbac-steps
    - ge-structured-content-pilot
  ai-usage: ai-assisted
title: |
  Use system-assigned managed identities to access Azure Cosmos DB data
introduction: |
  [!INCLUDE[NoSQL](includes/appliesto-nosql.md)]

  In this article, you'll set up a *robust, key rotation agnostic* solution to access Azure Cosmos DB keys by using [managed identities](../active-directory/managed-identities-azure-resources/services-support-managed-identities.md) and [data plane role-based access control](how-to-setup-rbac.md). The example in this article uses Azure Functions, but you can use any service that supports managed identities.

  You'll learn how to create a function app that can access Azure Cosmos DB data without needing to copy any Azure Cosmos DB keys. The function app will trigger when an HTTP request is made and then list all of the existing databases.

prerequisites:
  summary: |
    - An Azure account with an active subscription. [Create an account for free](https://azure.microsoft.com/free/?WT.mc_id=A261C142F).
    - An existing Azure Cosmos DB API for NoSQL account. [Create an Azure Cosmos DB API for NoSQL account](nosql/quickstart-portal.md)
    - An existing Azure Functions function app. [Create your first function in the Azure portal](../azure-functions/functions-create-function-app-portal.md)
      - A system-assigned managed identity for the function app. [Add a system-assigned identity](../app-service/overview-managed-identity.md#add-a-system-assigned-identity)
    - [Azure Functions Core Tools](../azure-functions/functions-run-local.md)
    - To perform the steps in this article, install the [Azure CLI](/cli/azure/install-azure-cli) and [sign in to Azure](/cli/azure/authenticate-azure-cli).
  
      ## Prerequisite check
      1. In a terminal or command window, store the names of your Azure Functions function app, Azure Cosmos DB account and resource group as shell variables named ``functionName``, ``cosmosName``, and ``resourceGroupName``.

          ```azurecli-interactive
          # Variable for function app name
          functionName="msdocs-function-app"
          
          # Variable for Azure Cosmos DB account name
          cosmosName="msdocs-cosmos-app"

          # Variable for resource group name
          resourceGroupName="msdocs-cosmos-functions-dotnet-identity"
          ```

          > [!NOTE]
          > These variables are reused in later steps. This example assumes your Azure Cosmos DB account name is ``msdocs-cosmos-app``, your function app name is ``msdocs-function-app`` and your resource group name is ``msdocs-cosmos-functions-dotnet-identity``.
      
      2. View the function app's properties using the [``az functionapp show``](/cli/azure/functionapp#az-functionapp-show) command.

          ```azurecli-interactive
          az functionapp show \
              --resource-group $resourceGroupName \
              --name $functionName
          ```
      
      3. View the properties of the system-assigned managed identity for your function app using [``az webapp identity show``](/cli/azure/webapp/identity#az-webapp-identity-show).

          ```azurecli-interactive
          az webapp identity show \
              --resource-group $resourceGroupName \
              --name $functionName
          ```
      
      4. View the Azure Cosmos DB account's properties using [``az cosmosdb show``](/cli/azure/cosmosdb#az-cosmosdb-show).

          ```azurecli-interactive
          az cosmosdb show \
              --resource-group $resourceGroupName \
              --name $cosmosName
          ```
procedureSection:
  - title: |
      Create Azure Cosmos DB API for NoSQL databases
    summary: |
      In this step, you create two databases.
    steps:
      - |
        In a terminal or command window, create a new ``products`` database using [``az cosmosdb sql database create``](/cli/azure/cosmosdb/sql/database#az-cosmosdb-sql-database-create).

          ```azurecli-interactive
          az cosmosdb sql database create \
              --resource-group $resourceGroupName \
              --name products \
              --account-name $cosmosName
          ```
      - |
        Create a new ``customers`` database.

          ```azurecli-interactive
          az cosmosdb sql database create \
              --resource-group $resourceGroupName \
              --name customers \
              --account-name $cosmosName
          ```
  - title: |
      Get Azure Cosmos DB API for NoSQL endpoint
    summary: |
      In this step, you query the document endpoint for the API for NoSQL account.
    steps:
      - |
        Use ``az cosmosdb show`` with the **query** parameter set to ``documentEndpoint``. Record the result. You'll use this value in a later step.

          ```azurecli-interactive
          az cosmosdb show \
              --resource-group $resourceGroupName \
              --name $cosmosName \
              --query documentEndpoint

          cosmosEndpoint=$(
              az cosmosdb show \
                  --resource-group $resourceGroupName \
                  --name $cosmosName \
                  --query documentEndpoint \
                  --output tsv
          )
          
          echo $cosmosEndpoint
          ```

          > [!NOTE]
          > This variable is reused in a later step.
  - title: |
      Grant access to your Azure Cosmos DB account
    summary: |
      In this step, you assign a role to the function app's system-assigned managed identity. Azure Cosmos DB has multiple built-in roles that you can assign to the managed identity for control-plane access. For data-plane access, you create a new custom role with access to read metadata.

      > [!TIP]
      > For more information about the importance of least privilege access, see the [Lower exposure of privileged accounts](../security/fundamentals/identity-management-best-practices.md#lower-exposure-of-privileged-accounts) article.
    steps:
      - |
        Use ``az cosmosdb show`` with the **query** parameter set to ``id``. Store the result in a shell variable named ``scope``.

          ```azurecli-interactive
          scope=$(
              az cosmosdb show \
                  --resource-group $resourceGroupName \
                  --name $cosmosName \
                  --query id \
                  --output tsv
          )
          
          echo $scope
          ```

          > [!NOTE]
          > This variable is reused in a later step.
      - |
        Use ``az webapp identity show`` with the **query** parameter set to ``principalId``. Store the result in a shell variable named ``principal``.

          ```azurecli-interactive
          principal=$(
              az webapp identity show \
                  --resource-group $resourceGroupName \
                  --name $functionName \
                  --query principalId \
                  --output tsv
          )
          
          echo $principal
          ```
      - |
        Create a new JSON file with the configuration of the new custom role.

          ```json
          {
              "RoleName": "Read Azure Cosmos DB Metadata",
              "Type": "CustomRole",
              "AssignableScopes": ["/"],
              "Permissions": [{
                  "DataActions": [
                      "Microsoft.DocumentDB/databaseAccounts/readMetadata"
                  ]
              }]
          }
          ```

          > [!TIP]
          > You can create a file in the Azure Cloud Shell using either `touch <filename>` or the built-in editor (`code .`). For more information, see [Azure Cloud Shell editor](../cloud-shell/using-cloud-shell-editor.md)
      - |
        Use [``az cosmosdb sql role definition create``](/cli/azure/cosmosdb/sql/role/definition#az-cosmosdb-sql-role-definition-create) to create a new role definition named ``Read Azure Cosmos DB Metadata`` using the custom JSON object.

          ```azurecli-interactive
          az cosmosdb sql role definition create \
              --resource-group $resourceGroupName \
              --account-name $cosmosName \
              --body @definition.json
          ```

          > [!NOTE]
          > In this example, the role definition is defined in a file named **definition.json**.
      - |
        Use [``az role assignment create``](/cli/azure/cosmosdb/sql/role/assignment#az-cosmosdb-sql-role-assignment-create) to assign the ``Read Azure Cosmos DB Metadata`` role to the system-assigned managed identity.

          ```azurecli-interactive
          az cosmosdb sql role assignment create \
              --resource-group $resourceGroupName \
              --account-name $cosmosName \
              --role-definition-name "Read Azure Cosmos DB Metadata" \
              --principal-id $principal \
              --scope $scope
          ```
  - title: |
      Programmatically access the Azure Cosmos DB keys
    summary: |
      We now have a function app that has a system-assigned managed identity with the custom role. The following function app will query the Azure Cosmos DB account for a list of databases.
    steps:
      - |
        Create a local function project with the ``--dotnet`` parameter in a folder named ``csmsfunc``. Change your shell's directory

          ```azurecli-interactive
          func init csmsfunc --dotnet
          
          cd csmsfunc
          ```
      - |
        Create a new function with the **template** parameter set to ``httptrigger`` and the **name** set to ``readdatabases``.

          ```azurecli-interactive
          func new --template httptrigger --name readdatabases
          ```
      - |
        Add the [``Azure.Identity``](https://www.nuget.org/packages/Azure.Identity/) and [``Microsoft.Azure.Cosmos``](https://www.nuget.org/packages/Microsoft.Azure.Cosmos/) NuGet package to the .NET project. Build the project using [``dotnet build``](/dotnet/core/tools/dotnet-build).

          ```azurecli-interactive
          dotnet add package Azure.Identity
          
          dotnet add package Microsoft.Azure.Cosmos
          
          dotnet build
          ```
      - |
        Open the function code in an integrated developer environment (IDE).

          > [!TIP]
          > If you are using the Azure CLI locally or in the Azure Cloud Shell, you can open Visual Studio Code.
          >
          > ```azurecli
          > code .
          > ```
          >
      - |
        Replace the code in the **readdatabases.cs** file with this sample function implementation. Save the updated file.

          ```csharp
          using System;
          using System.Collections.Generic;
          using System.Threading.Tasks;
          using Azure.Identity;
          using Microsoft.AspNetCore.Mvc;
          using Microsoft.Azure.Cosmos;
          using Microsoft.Azure.WebJobs;
          using Microsoft.Azure.WebJobs.Extensions.Http;
          using Microsoft.AspNetCore.Http;
          using Microsoft.Extensions.Logging;
          
          namespace csmsfunc
          {
              public static class readdatabases
              {
                  [FunctionName("readdatabases")]
                  public static async Task<IActionResult> Run(
                      [HttpTrigger(AuthorizationLevel.Anonymous, "get")] HttpRequest req,
                      ILogger log)
                  {
                      log.LogTrace("Start function");
          
                      CosmosClient client = new CosmosClient(
                          accountEndpoint: Environment.GetEnvironmentVariable("COSMOS_ENDPOINT", EnvironmentVariableTarget.Process),
                          new DefaultAzureCredential()
                      );
          
                      using FeedIterator<DatabaseProperties> iterator = client.GetDatabaseQueryIterator<DatabaseProperties>();
          
                      List<(string name, string uri)> databases = new();
                      while(iterator.HasMoreResults)
                      {
                          foreach(DatabaseProperties database in await iterator.ReadNextAsync())
                          {
                              log.LogTrace($"[Database Found]\t{database.Id}");
                              databases.Add((database.Id, database.SelfLink));
                          }
                      }
          
                      return new OkObjectResult(databases);
                  }
              }
          }
          ```
  - title: |
      (Optional) Run the function locally
    summary: |
      In a local environment, the [``DefaultAzureCredential``](/dotnet/api/azure.identity.defaultazurecredential) class uses various local credentials to determine the current identity. While running locally isn't required for the how-to, you can develop locally using your own identity or a service principal.
    steps:
      - |
        Get your local account's principal identifier using [`az ad signed-in-user show`](/cli/azure/ad/signed-in-user#az-ad-signed-in-user-show).

        ```azurecli-interactive
        az ad signed-in-user show --query "id"
        ```
      - |
        Assign your local account role-based access control access to the Azure Cosmos DB account using [`az cosmosdb sql role assignment create`](/cli/azure/cosmosdb/sql/role/assignment#az-cosmosdb-sql-role-assignment-create) command. Use the built-in "Cosmos DB Data Contributor" role with an id of `00000000-0000-0000-0000-000000000002`.

        ```azurecli-interactive
        az cosmosdb sql role assignment create \
            --resource-group $resourceGroupName \
            --account-name $cosmosName \
            --role-definition-id "00000000-0000-0000-0000-000000000002" \
            --principal-id "<your-principal-id>" \
            --scope "/"
        ```
      - |
        In the **local.settings.json** file, add a new setting named ``COSMOS_ENDPOINT`` in the **Values** object. The value of the setting should be the document endpoint you recorded earlier in this how-to guide.

          ```json
          ...
          "Values": {
              ...
              "COSMOS_ENDPOINT": "https://msdocs-cosmos-app.documents.azure.com:443/",
              ...
          }
          ...
          ```

          > [!NOTE]
          > This JSON object has been shortened for brevity. This JSON object also includes a sample value that assumes your account name is ``msdocs-cosmos-app``.
      - |
        Run the function app

          ```azurecli
          func start
          ```
  - title: |
      Deploy to Azure
    summary: |
      Once published, the ``DefaultAzureCredential`` class uses credentials from the environment or a managed identity. For this guide, the system-assigned managed identity will be used as a credential for the [``CosmosClient``](/dotnet/api/microsoft.azure.cosmos.cosmosclient) constructor.
    steps:
      - |
        Set the ``COSMOS_ENDPOINT`` setting on the function app already deployed in Azure.

          ```azurecli-interactive
          az functionapp config appsettings set \
              --resource-group $resourceGroupName \
              --name $functionName \
              --settings "COSMOS_ENDPOINT=$cosmosEndpoint"
          ```
      - |
        Deploy your function app to Azure by reusing the ``functionName`` shell variable:

          ```azurecli-interactive
          func azure functionapp publish $functionName
          ```
      - |
        [Test your function in the Azure portal](../azure-functions/functions-create-function-app-portal.md#test-the-function).
relatedContent:
  - text: Secure Azure Cosmos DB keys using Azure Key Vault
    url: store-credentials-key-vault.md
  - text: Security baseline for Azure Cosmos DB
    url: security-baseline.md