Authenticate Python apps to Azure services during local development using service principals
When creating cloud applications, developers need to debug and test applications on their local workstation. When an application is run on a developer's workstation during local development, it still must authenticate to any Azure services used by the app. This article covers how to set up dedicated application service principal objects to be used during local development.
Dedicated application service principals for local development allow you to follow the principle of least privilege during app development. Since permissions are scoped to exactly what is needed for the app during development, app code is prevented from accidentally accessing an Azure resource intended for use by a different app. This also prevents bugs from occurring when the app is moved to production because the app was overprivileged in the dev environment.
An application service principal is set up for the app when the app is registered in Azure. When registering apps for local development, it's recommended to:
- Create separate app registrations for each developer working on the app. This will create separate application service principals for each developer to use during local development and avoid the need for developers to share credentials for a single application service principal.
- Create separate app registrations per app. This scopes the app's permissions to only what is needed by the app.
During local development, environment variables are set with the application service principal's identity. The Azure SDK for Python reads these environment variables and uses this information to authenticate the app to the Azure resources it needs.
1 - Register the application in Azure
Application service principal objects are created with an app registration in Azure. This can be done using either the Azure portal or Azure CLI.
Sign in to the Azure portal and follow these steps.
2 - Create an Azure AD security group for local development
Since there typically multiple developers who work on an application, it's recommended to create an Azure AD group to encapsulate the roles (permissions) the app needs in local development rather than assigning the roles to individual service principal objects. This offers the following advantages.
- Every developer is assured to have the same roles assigned since roles are assigned at the group level.
- If a new role is needed for the app, it only needs to be added to the Azure AD group for the app.
- If a new developer joins the team, a new application service principal is created for the developer and added to the group, assuring the developer has the right permissions to work on the app.
3 - Assign roles to the application
Next, you need to determine what roles (permissions) your app needs on what resources and assign those roles to your app. In this example, the roles will be assigned to the Azure Active Directory group created in step 2. Roles can be assigned a role at a resource, resource group, or subscription scope. This example will show how to assign roles at the resource group scope since most applications group all their Azure resources into a single resource group.
4 - Set local development environment variables
DefaultAzureCredential object will look for the service principal information in a set of environment variables at runtime. Since most developers work on multiple applications, it's recommended to use a package like python-dotenv to access environment from a
.env file stored in the application's directory during development. This scopes the environment variables used to authenticate the application to Azure such that they can only be used by this application.
.env file is never checked into source control since it contains the application secret key for Azure. The standard .gitignore file for Python automatically excludes the
.env file from check-in.
To use the python-dotenv package, first install the package in your application.
pip install python-dotenv
Then, create a
.env file in your application root directory. Set the environment variable values with values obtained from the app registration process as follows:
AZURE_CLIENT_ID→ The app ID value.
AZURE_TENANT_ID→ The tenant ID value.
AZURE_CLIENT_SECRET→ The password/credential generated for the app.
AZURE_CLIENT_ID=00000000-0000-0000-0000-000000000000 AZURE_TENANT_ID=11111111-1111-1111-1111-111111111111 AZURE_CLIENT_SECRET=abcdefghijklmnopqrstuvwxyz
Finally, in the startup code for your application, use the
python-dotenv library to read the environment variables from the
.env file on startup.
from dotenv import load_dotenv if ( os.environ['ENVIRONMENT'] == 'development'): print("Loading environment variables from .env file") load_dotenv(".env")
5 - Implement DefaultAzureCredential in your application
To authenticate Azure SDK client objects to Azure, your application should use the
DefaultAzureCredential class from the
azure.identity package. In this scenario,
DefaultAzureCredential will detect the environment variables
AZURE_CLIENT_SECRET are set and read those variables to get the application service principal information to connect to Azure with.
Start by adding the azure.identity package to your application.
pip install azure-identity
Next, for any Python code that creates an Azure SDK client object in your app, you'll want to:
- Import the
DefaultAzureCredentialclass from the
- Create a
- Pass the
DefaultAzureCredentialobject to the Azure SDK client object constructor.
An example of this is shown in the following code segment.
from azure.identity import DefaultAzureCredential from azure.storage.blob import BlobServiceClient # Acquire a credential object token_credential = DefaultAzureCredential() blob_service_client = BlobServiceClient( account_url="https://<my_account_name>.blob.core.windows.net", credential=token_credential)
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