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The Consumer Secret is also shared with and possible possibly arrived at via negotiation with the TC. The SSP TP implementation enforces no strength restrictions on this field other than that it must be non-empty. But it should be at least as strong as whatever requirements are placed on end-user passwords and likely stronger than that, since it is used for establishing an application-to-application trust relationship that allows the TC to assume the identity of any user. Because of the nature of LTI security, this value must be stored in plain text in both the TP and TC.
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