Tokens: Adding AccessToken class for storing accessTokens for OAuth2

lib/api/models/access_token.dart

@@ -0,0 +1,30 @@
+// coverage:ignore-file
+
+class AccessToken {
+  final String accessToken;
+  final String tokenType;
+  final int expiresIn;
+  final String membershipId;
+
+  const AccessToken({
+    required this.accessToken,
+    required this.tokenType,
+    required this.expiresIn,
+    required this.membershipId
+  });
+
+  AccessToken.fromJson(Map<String, dynamic> json) :
+      accessToken = json["access_token"],
+      tokenType = json["token_type"],
+      expiresIn = json["expires_in"],
+      membershipId = json["membership_id"];
+
+  Map<String, dynamic> toJson() {
+    return <String, dynamic>{
+      "access_token": accessToken,
+      "token_type": tokenType,
+      "expires_in": expiresIn,
+      "membership_id": membershipId
+    };
+  }
+}