In what circumstances will a confession be inadmissible if it is obtained by force or threat of violence?

Similarly, it is to be observed that the rule, as stated in Ibrahim v. The King, supra, is confined to confessions made to persons in authority. If the subjective test is resorted to to determine whether the confession was made to a person in authority, then it would follow that the officer in question was not a person in authority, and the confession would be admitted even though under some other guise the police officer had obtained it by force or threat of violence. In my respectful opinion, if the statement were obtained under such circumstances, it would be inadmissible once it was shown that the person obtaining such a statement was in fact a police officer even though such fact was unknown to the accused.