1. A system comprising: a client device in communication via a network with a server and a common gateway interface; a native app executing on one or more hardware processors of the client device to receive a device session token from the server for authenticating a device session between the native app and the server, the device session token including credentials authenticating a user for a device session between the server and the native app executing on the client device; and an embedded web browser executing on one or more hardware processors of the client device, wherein: the native app invokes the embedded web browser and the native app passes the device session token to the embedded web browser for authentication of a web session between the embedded web browser and the common gateway interface that continues the device session authentication without requiring additional authentication; and the embedded web browser passes the device session token to the common gateway interface and receives from the common gateway interface a web flow authorization token, converted from the device session token using the credentials for authenticating the user for the device session between the server and the native app executing on the client device, for authenticating the web session as a continuation of the device session authenticated by the device session token so that the web flow authorization token and the device session token both share the same underlying device session and the device session remains active while the web session is active.