Since your question has zero details I’m going to answer it in a personal way, the authenticity of the Buddha’s teaching. As the Buddha taught, one of his disciples Ananda was able to memorize them through the repetitive manner that the Buddha framed his speeches. During the first Buddhist council Ananda was the primary monastic responsible for orally reciting the Buddha’s teachings to confirm everyone heard it correctly.

Over the next couple hundred years these oral traditions shifting to a written one while maintaining the same format. Many sutras start with “Thus have I heard” as that is how Ananda recited the teachings during the Buddha’s life and at the first Buddhist council.

When Mahayana Buddhism came into being slowly many new sutras appeared which would include two methods of confirming for their readers their authentic status. One was to being the texts with “Thus have I heard” to call back to the Buddha’s disciple Ananda. It must be true if you can trace it to someone who knew him personally! Two was to self reference the importance and level of the teaching within the text, such as the Heart Sutra describing its own mantra as the highest, and the Lotus Sutra describing the Lotus Sutra as the highest sutra in a very meta manner.

Another method that Mahayana writers and teachings use is to say they’re not from the historical Buddha. The most famous sutra, the heart sutra, is framed as Guanyin, Avalokitesvara, teaching to Sariputra.

So forgeries were prevented by calling on people or beings of religious importance and including the sutras importance and thus authenticity within the text itself.

The advent of western scholarship on Buddhist studies created a crisis especially in East Asian Mahayana schools who began to doubt the authenticity of their own teachers. This first was imported into Japan through their early contact with the West then America in the 19th century. Richard Jaffe’s Seeming Sakyamuni is about these Japanese priests doubting Japanese Buddhism authenticity to the point of traveling all the way to Sri Lanka and Indian where sutra weren’t adding methods of authenticity within the texts.

These western ideas were passed through Japan into China where there was a lesser but similar reaction through figures such as Ouyang Jian wanting to go back to Indian Buddhism.