Different Christian churches or denominations have a different 'bottom line' as regards authority - the source of truth; but all are vulnerable to corruption of that source. And indeed all the main denominations have indeed been corrupted in this way.
Eastern Orthodoxy relied on an unbroken transmission of oral, personal tradition from the times of the Church Fathers; but that has been broken - especially by the Russian Revolution. By the standards the church established for itself; what is broken cannot be restored. Modern Eastern Orthodoxy, in most of the world, is cut-off from its roots - the chain of master and apprentice, the unquestioned authority of spiritual fathers... these are gone.
The Roman Catholic church has developed a different model of authority based upon the figure of the Pope; from whom comes the authority of the church via the bishops whom he appoints. It is a top-down system. But when first the bishops, then the Pope, become corrupted by politics and other priorities; then corruption instead of holiness moves from the top down - and there is no (human) mechanism for correction.
The Protestant churches mostly based their authority on scripture, on the Bible; but did not tie authority to any specific translation or interpretation - the truth was supposed to shine-through any version. But there has been a massive proliferation of translations; many of them corrupted by worldly, sexual and political agendas. Scripture has lost its meaning, its cohesion, its dependability.
A cross-denominational source of authority is 'theology', broadly understood - reasoned discourse. The Roman Catholic church took this to the highest level with scholasticism and a special role of Thomas Aquinas - but this was no sooner achieved by Aquinas then demolished, confused, complicated and made incoherent by subsequent generations - and this has by now reached an extreme state.
In general, Theology has become became increasingly secular, academic and fashion-driven in its assumptions and methods - and is useless, indeed counter-productive, as a source of authority.
If there is supposed to be an 'expertise' in understanding scripture, church tradition, and the structure of religious authority - then this expertise points almost everywhere all at once.
My personal conclusion is that the serious Christian - here and now - is confronted by an already-existing system in which living from external authority of any kind and of all kinds has become an impossibility - however much we might want it.
The thing about religious authority is that it cannot be created consciously. Pascal saw this more than 400 years ago at the beginning of modernity.
Or: authority used to be implicit, spontaneous, taken-for granted. When authority became conscious and a matter of choice - then it ceased to be primary; and the conscious act of choice (and whatever guides that) became primary.
Authority can only be built onto authority - so we each must consciously find (because nothing could be more important) what we really, actually, in implicit practice, regard as true and real: and then built from that, and from nothing else.
No matter that this is not given us by The World; we can have faith that if we are honest and diligent in this quest, then our loving God will ensure that we will find what we need.