1. A system for concealing tenancy in a multi-tenant cloud service relying on federated identities, said system comprising: a memory area associated with a cloud service, said memory area storing a set of tenant identifiers each corresponding to one of a plurality of tenants of the cloud service; and a processor programmed to: receive a request for a document from a first entity by the cloud service, the request including an identifier associated with a second entity; receive, from an identity provider, a token authenticating the first entity; compare the identifier to a set of tenant identifiers each corresponding to one of the plurality of tenants to determine whether the second entity is one of the plurality of tenants; dynamically generate a fictitious document on determining that the second entity is not one of the plurality of tenants; digitally sign the generated fictitious document with a certificate for the second entity; and send the signed fictitious document to the first entity.