spark.hadoop.fs.azure.account.key.<storage_account>.dfs.core.windows.net <key>
This key is associated with the storage account to be used. You can
                        find it in the Access keys blade of this storage account. Two
                        keys are available for each account and by default, either of them
                        can be used for this access.
               Ensure that the account to be used has the appropriate read/write
                        rights and permissions.