
Samsung Galaxy A8(2016)
Every official firmware build for SM-A810S, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/A810SKST2CTI1
Specifications of SM-A810F, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-A810F

SM-A800X

SM-A715X

SM-A710X

SM-A826S
You can find the firmware on the model: SM-A810S page.
Yes, all firmware files for SM-A810S are 100% official, original, and obtained directly from Samsung servers.
To flash SM-A810S, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SM-A810S.