feat(domain): add DID standard model

Domain/Sources/Models/DID.swift

@@ -0,0 +1,29 @@
+import Foundation
+
+public typealias DIDMethod = String
+public typealias DIDMethodId = String
+
+/// Represents a DID with ``DIDMethod`` and ``DIDMethodId``
+/// As specified in `https://www.w3.org/TR/did-core/#dfn-did-schemes`
+public struct DID {
+    public let schema: String
+    public let method: DIDMethod
+    public let methodId: DIDMethodId
+
+    /// Initializes a standard DID
+    /// - Parameters:
+    ///   - schema: By default it will be `did` as standard.
+    ///   - method: DIDMethod specification
+    ///   - methodId: DIDMethodId
+    public init(
+        schema: String = "did",
+        method: DIDMethod,
+        methodId: DIDMethodId
+    ) {
+        self.schema = schema
+        self.method = method
+        self.methodId = methodId
+    }
+
+    public var string: String { "\(schema):\(method):\(methodId)" }
+}