Is Raza (permission) of authoritative leader/caliph/Imam required to lead prayers in Islam? Assuming the leader/Amir exists among us.
Your question a little seems to be vague. But if I've perceived well, in case that you mean if Raza (permission) of authoritative leader/caliph/Imam required to lead prayers in Islam for a person to be counted as a Imam of Jama’a and as a representative of Shar’, the reply could be yes, and he ought to have the permission of Hakem-al-Shar’ in order to being as an agent of the Shar’.
But solely being as an Imam for Salah-a-Jama’a it doesn’t seem wajib to have the permission of leader/caliph/Imam. Although there are some conditions for being the Imam of Jama’ that the Imam and persons who prayers behind him, ought to note those conditions in order to have correct Salahs.