ircd:Ⓜ️ Structure for CrossSignKey.

include/ircd/m/device.h

@@ -16,8 +16,34 @@ namespace ircd::m
 	struct device;
 	struct device_keys;
 	struct device_list_update;
+	struct cross_signing_key;
 }
 
+struct ircd::m::cross_signing_key
+:json::tuple
+<
+	/// Required. The ID of the user the key belongs to.
+	json::property<name::user_id, json::string>,
+
+	/// Required. What the key is used for.
+	/// One of: ["master", "self_signing", "user_signing"]
+	json::property<name::usage, json::string>,
+
+	/// Required. The public key. The object must have exactly one property,
+	/// whose name is in the form <algorithm>:<unpadded_base64_public_key>,
+	/// and whose value is the unpadded base64 public key.
+	json::property<name::keys, json::object>,
+
+	/// Signatures of the key, calculated using the process described at
+	/// Signing JSON. Optional for the master key. Other keys must be signed
+	/// by the user's master key.
+	json::property<name::signatures, json::object>
+>
+{
+	using super_type::tuple;
+	using super_type::operator=;
+};
+
 struct ircd::m::device_keys
 :json::tuple
 <

include/ircd/m/name.h

@@ -209,4 +209,6 @@ struct ircd::m::name
 	static constexpr const char *const msgtype {"msgtype"};
 	static constexpr const char *const format {"format"};
 	static constexpr const char *const formatted_body {"formatted_body"};
+
+	static constexpr const char *const usage {"usage"};
 };

matrix/name.cc

@@ -188,3 +188,5 @@ constexpr const char *const ircd::m::name::body;
 constexpr const char *const ircd::m::name::msgtype;
 constexpr const char *const ircd::m::name::format;
 constexpr const char *const ircd::m::name::formatted_body;
+
+constexpr const char *const ircd::m::name::usage;