AUTH properties

The last field in the Variable header of AUTH packet is a set of Properties. A set contains a Property Length followed by the Properties. A Property consists of an Identifier and a value.

This section lists all possible AUTH Properties and describes their usage:

Table 1.17. AUTH properties

Identifier	Value type	Description
authentication_method	`std::string`	A UTF-8 Encoded String containing the name of the authentication method used for extended authentication.
authentication_data	`std::string`	Binary Data containing authentication data. The contents of the data are defined by the authentication method.
reason_string	`std::string`	A UTF-8 Encoded String representing the reason associated with this response.
user_property	`std::pair<std::string, std::string>`	Name, value pair (`UTF-8 String Pair`) defining User Property. There can be multiple pairs in one packet. This property may be used to provide additional diagnostic or other information.

Usage

After obtaining an instance of async_mqtt5::auth_props, the subscript operator can be used to access a Property.

The Identifiers listed in the table above are available within the async_mqtt5::prop namespace for Property access.

	Note
	When accessing a property value, the subscript operator will return a `std::optional` of the value type for all properties, except for `async_mqtt5::prop::user_property`, where it will return an instance of `std::vector<std::pair<std::string, std::string>>`.

Example

The following example shows how to set a Property value:

async_mqtt5::auth_props props;
props[async_mqtt5::prop::authentication_method] = "SCRAM-SHA-1";
props[async_mqtt5::prop::authentication_data] = "data";
props[async_mqtt5::prop::user_property].emplace_back("name", "value");

The following example shows how to retrieve a Property value:

std::optional<std::string> auth_data = props[async_mqtt5::prop::authentication_data];
if (auth_data.has_value())
	// authentication data property was previously set
else
	// authentication data property was not set

std::vector<std::pair<std::string, std::string>>& user_props = props[async_mqtt5::prop::user_property];
if (!user_props.empty())
	// user property was previously set
else
	// user property was not set