What is Azure Service Principal?

Question

My requirement is simple. I want to login to Azure through my shell script in non-interactive mode, but "az login -u username -p password" command gives the following error:

Get Token request returned http error: 400 and server response: {"error":"invalid_grant","error_description":"AADSTS70002: Error validating credentials. : SAML token is invalid. : The element with ID 'xxxxxx' was either unsigned or the signature was invalid. 

Some site told me to create a service principal. Now my question is, what is a service principal, and how do I create a service principal so that I can execute my commands (for creating different resources like app gateway) from my shell script?

Answer 1

Please refer to this official document.

An Azure service principal is a security identity used by user-created apps, services, and automation tools to access specific Azure resources. Think of it as a 'user identity' (login and password or certificate) with a specific role, and tightly controlled permissions to access your resources. It only needs to be able to do specific things, unlike a general user identity. It improves security if you only grant it the minimum permissions level needed to perform its management tasks.

If you want to create a new service principal(sp) with Azure CLi 2.0. You could login with your Azure AD user. Then execute following command.

az ad sp create-for-rbac --name {appId} --password "{strong password}" 

The result like below:

{   "appId": "a487e0c1-82af-47d9-9a0b-af184eb87646d",   "displayName": "MyDemoWebApp",   "name": "http://MyDemoWebApp",   "password": {strong password},   "tenant": "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX" } 

appId is your login user, password is login password.

After the sp is created, you also need give it Contributor role, then you could manage your Azure resource.

az role assignment create --assignee <objectID> --role Contributor 

Now, you could login in non interctive mode with following command.

az login --service-principal -u <appid> --password {password-or-path-to-cert} --tenant {tenant} 

Answer 2

Service principal just work as an impersonation for user in Azure AD. Refer - https://sanganakauthority.blogspot.com/2019/04/how-to-create-service-principal-or-app.html

Using this you can perform any type of management task against Azure using REST APIs. This way you avoid need of providing credentials in pop up and hence help to automate things in Azure using REST APIs.