Service providing system, service delivery system, service providing method, and non-transitory recording medium

A service providing method executed by a service providing system that, at a time of providing a service to a communication terminal, causes an authentication system to authenticate a user of the communication terminal, the service providing method comprising:

• associating with one another by a processor a plurality of pieces of terminal identification information for identifying different communication terminals common to a same user and managing the plurality of pieces of terminal identification information, each of the plurality of pieces of terminal identification information including user identification information having a to-be-authenticated section to be used to authenticate a terminal identification of the user and is common to the plurality of pieces of terminal identification information and a not to-be-authenticated section not to be used to authenticate the terminal identification of the user, the processor managing and associating the plurality of pieces of terminal identification information with one another as a piece of terminal identification information for a communication source and a piece of terminal identification information for a communication destination that can perform communication with the communication source;
• receiving by a processor from a first communication terminal as a communication source a first piece of terminal identification information for identifying the first communication terminal and a second piece of terminal identification information for identifying a second communication terminal as a communication destination;
• and
• in response to receiving the first piece of terminal identification information and the second piece of terminal identification information, transmitting by a processor a request to the second communication terminal to start communication with the first communication terminal thereby allowing control of the second communication terminal from the first communication terminal for a case where the first piece of terminal identification information and the second piece of terminal identification information are managed and associated with one another and not transmitting a request to the second communication terminal to start communication with the first communication terminal for a case where the first piece of terminal identification information and the second piece of terminal identification information are not managed as being associated with one another.