To back up Azure Blob Storage data with object storage, you need to add at least one object storage repository. To define the content of the backup, you need to configure the content groups for the object storage repositories.
To add an Azure Blob Storage object storage repository, consider the scenarios that you have and then choose an authentication method.
If you want to back up storage containers using access and secret keys, then use access and secret keys to add the Azure Blob Storage object storage repository.
If an Azure virtual machine (VM) can be authorized to access the Azure Blob Storage account to be backed up, and both the VM and the storage account are in the same Azure environment, then you can use the storage blob data owner role to authenticate the account on this Azure VM, which you can also set up as access node.
If you are going to to back up the Azure Blob Storage account with a use a non-Azure VM as access node, then to authenticate the account, you need to create an Azure AD application and assign the storage blob owner role to that application.