azure-iot-sdk-python/doc/sk_authentication_provider.md

Overview

The SymmetricKeyAuthenticationProvider class represents a type of AuthenticationProvider which can accept a connection string. The authentication provider is created by first parsing the connection string. HostName=;DeviceId=<device_id>;ModuleId=<module_id>;SharedAccessKey=<shared_access_key>;SharedAccessKeyName=<key_name> For a device connection string the parsed fields are :- HostName, DeviceId , SharedAccessKey, and an optional SharedAccessKeyName. For a module connection string the parsed fields are :- HostName, DeviceId , ModuleId, SharedAccessKey, and an optional SharedAccessKeyName.

Private Dunder Init

Creates a new instance of the SymmetricKeyAuthenticationProvider object. It takes in parameters hostname, device_id, optional module_id and sas_token_str.

hostname : Hostname of the Azure IoT hub.
device_id: Identifier for the device
module_id: Identifier for the module on the device
sas_token_str: the string representation of the shared access signature already passed in by the user.

Static Method

The static method parse is overridden from the base class and is responsible for parsing out the different attributes in the passed in connection string.

parse(connection_string) [static]

The parse static method takes in a string representation of the entire connection information which is already available to the user. The string format looks like one of the options below.

• HostName=<hostname>;DeviceId=<device_id>;SharedAccessKey=<shared_access_key>
• HostName=<hostname>;DeviceId=<device_id>;SharedAccessKey=<shared_access_key>;SharedAccessKeyName=<key_name>
• HostName=<hostname>;DeviceId=<device_id>;ModuleId=<module_id>;SharedAccessKey=<shared_access_key>;SharedAccessKeyName=<key_name>

The parse method is responsible for the following :-

• Parses the 'name=value' field found in source.
• Validates the information present in the source.
• Creates a base64-encoded HMAC-SHA256 hash of the string to sign.
• Create the resource uri and quotes it as well.
• Then uses the resource uri, signature, optional key name and a default expiry of 1 hr to create a shared access signature string.
• Finally returns a new instance of the SymmetricKeyAuthenticationProvider object.

Instance method

The instance method get_current_sas_token gives back the current shared access signature string.

Helper Methods

• _validate_keys : This private helper method validates the correct combination of the name, value pairs in the string provided during parse.
• _signature : This private helper method creates the hash to provide the sig portion of the shared access signature string.
• _create_sas : Creates the shared access signature string.