What is claimed is:1. A method for authentication of user devices, the method comprising:performing an authentication of a first user device to a media device, wherein:an authentication token that indicates an identity of the media device is associated with the authentication of the first user device to the media device, andan identifier of the first user device is included in an access control list maintained by a server system, wherein the access control list indicates devices that are authenticated and provided with media playback control on the media device;identifying, using the first user device, a second user device in proximity to the first user device;transmitting, using the first user device to the second user device, an invitation message to authenticate the second user device to the media device, wherein:interaction with the invitation message causes the authentication token to be transferred from the first user device to the second user device,the authentication token is transmitted by the second user device to the server system to authenticate the second user device to the media device,the second user device is added to the access control list maintained by the server system, andafter the second user device has been authenticated by being added to the access control list, a media content item selected using the second user device is transmitted to the media device for playback; andremoving, by the server system, the second user device from the access control list maintained by the server system based on proximity of the second user device to the media device, whereinremoving the second user device from the access control list prevents the second user device from selecting media content items for playback by the media device.2. The method of claim 1, wherein the authentication token is stored on the server system in association with the identifier of the first user device.3. The method of claim 2, wherein the authentication token is used as a key in a key-value pair in connection with a corresponding access control list stored on the server system.4. The method of claim 1, further comprising:generating, using the first user device, the authentication token; andtransmitting the authentication token to a server.5. The method of claim 1, further comprising:transmitting, to a server, a request for the authentication token; andreceiving the authentication token from the server.6. The method of claim 1, further comprising receiving, from a contact list associated with a first user of the first user device, an indication of a second user of the second user device, wherein the second user device is identified based on the received indication.7. The method of claim 1, wherein identifying the second user device comprises detecting the second user device based on a connection to a communications network.8. The method of claim 1, wherein identifying the second user device comprises:detecting a movement of the first user device; andtransmitting, to a server, an indication of the movement and a first location associated with the first user device.9. The method of claim 8, further comprising receiving, from the server, an identifier associated with the second user device, wherein the second user device detected a movement of the second user device at a second location and wherein the first location and the second location are within a predetermined distance.10. The method of claim 1, further comprising:receiving, from a user of the first user device, an indication that the second user device is not to be authenticated to the media device; andtransmitting, to a server, a request to remove authentication permission for the second user device to the media device.11. A system for authentication of user devices, the system comprising:a hardware processor on a first user device that:performs an authentication of the first user device to a media device, wherein:an authentication token that indicates an identity of the media device is associated with the authentication of the first user device to the media device, andan identifier of the first user device is included in an access control list, wherein the access control list indicates devices that are authenticated and provided with media playback control on the media device upon authentication;identifies, using the first user device, a second user device in proximity to the first user device; andtransmits, using the first user device to the second user device, an invitation message to authenticate the second user device to the media device, wherein:interaction with the invitation message causes the authentication token to be transferred from the first user device to the second user device,the authentication token is used to authenticate the second user device to the media device,the second user device is added to the access control list maintained by a server system,after the second user device has been authenticated by being added to the access control list, a media content item selected using the second user device is transmitted to the media device for playback, andthe server system removes the second user device from the access control list based on proximity of the second user device to the media device, whereinremoving the second user device from the access control list prevents the second user device from selecting media content items for playback by the media device.12. The system of claim 11, wherein the authentication token is stored on the server system in association with the identifier of the first user device.13. The system of claim 12, wherein the authentication token is used as a key in a key-value pair in connection with a corresponding access control list stored on the server system.14. The system of claim 11, wherein the hardware processor also:generates, using the first user device, the authentication token; andtransmits the authentication token to a server.15. The system of claim 11, wherein the hardware processor also:transmits, to a server, a request for the authentication token; andreceives the authentication token from the server.16. The system of claim 11, wherein the hardware processor also receives, from a contact list associated with a first user of the first user device, an indication of a second user of the second user device, wherein the second user device is identified based on the received indication.17. The system of claim 11, wherein identifying the second user device comprises detecting the second user device based on a connection to a communications network.18. The system of claim 11, wherein identifying the second user device comprises:detecting a movement of the first user device; andtransmitting, to a server, an indication of the movement and a first location associated with the first user device.19. The system of claim 18, wherein the hardware processor also receives, from the server, an identifier associated with the second user device, wherein the second user device detected a movement of the second user device at a second location and wherein the first location and the second location are within a predetermined distance.20. The system of claim 11, wherein the hardware processor also:receives, from a user of the first user device, an indication that the second user device is not to be authenticated to the media device; andtransmits, to a server, a request to remove authentication permission for the second user device to the media device.21. A non-transitory computer-readable medium containing computer-executable instructions that, when executed by a processor, cause the processor to perform a method for authentication of user devices, the method comprising:performing an authentication of a first user device to a media device, wherein:an authentication token that indicates an identity of the media device is associated with the authentication of the first user device to the media device, andan identifier of the first user device is included in an access control list maintained by a server system, wherein the access control list indicates devices that are authenticated and provided with media playback control on the media device;identifying, using the first user device, a second user device in proximity to the first user device; andtransmitting, using the first user device to the second user device, an invitation message to authenticate the second user device to the media device, wherein:interaction with the invitation message causes the authentication token to be transferred from the first user device to the second user device,the authentication token is transmitted by the second user device to the server system to authenticate the second user device to the media device,the second user device is added to the access control list maintained by the server system, andafter the second user device has been authenticated by being added to the access control list, a media content item selected using the second user device is transmitted to the media device for playback, andthe server system removes the second user device from the access control list based on proximity of the second user device to the media device, whereinremoving the second user device from the access control list prevents the second user device from selecting media content items for playback by the media device.