| CPC H04L 63/0807 (2013.01) [H04L 63/126 (2013.01)] | 20 Claims |

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1. A token verification method performed by a service server, the method comprising:
receiving a service request message comprising a token from a client;
performing a first verification process for the token through local storage of the service server in response to the service request message; and
performing a second verification process for the token through another service server, selected among service servers that provided services, in response to failure of the first verification process,
wherein the services are sequentially used by the client prior to reception of the service request message, and
wherein the service request message further comprises a used service list of the client, the used service list including the services.
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