[Honor 8 Guides, News, & Discussion] hackslash:
WARNING: Flashing an unapproved firmware can cause unexpected issues. The OP will not be liable for any bricked device which resulted because of the use of this method. Everything is done at user's discretion. Also, ensure that you're using the correct firmware file (matches your model and is not corrupt).

Important notes for updating from Oreo -> Oreo

If you're on Oreo, don't download the recoveries mentioned in the guide below. Instead grab the one below (thanks to TeamMT for the patched recovery):

https://drive.google.com/open?id=1HmFAMYm1pU7RdKkOq_TMdthCxZJflzv9

Note that this is only 1 recovery. So whenever you see the command:

fastboot flash recovery FRD_RECOVERY_NoCheck.img

Replace it with:

fastboot flash recovery_ramdisk FRD_RECOVERY_RAMDISK_NoCheck.img

For recovery2:

fastboot flash erecovery_ramdisk FRD_RECOVERY_RAMDISK_NoCheck.img

I know it's the same recovery being flashed on two different partitions but it doesn't matters ;)

Happy flashing !

What will you achieve...

With this guide you can flash FullOTA-MF firmwares which are unapproved for installation (also called 'online firmwares', shows errors when flashing in TWRP or authentication errors when using Firmware Finder proxy) on your device by bypassing the authentication checks at stock recovery. PV (Point Version) firmwares should not be flashed by this method since they can be already flashed via TWRP.

I successfully updated my FRD-L09 from B392SP01 to B394. I'm writing down two methods, you can use any ;)

Method 1 Using RedLotus

RedLotus is an open source huawei proxy that allows you to push any update to your device through HiSuite.

A) PREPARATION / Device

Download the modified (NoCheck, authentication removed) stock recovery:

Recovery 1: https://drive.google.com/file/d/0B4SPRmBNsTefSWZLSWxpWGd6QkE/view?usp=drivesdk&resourcekey=0-cZTB6Ze_tUOaJsTPPvErYQ
Recovery 2: https://drive.google.com/file/d/0B4SPRmBNsTefSVhxMWFoa01wams/view?usp=drivesdk&resourcekey=0-DuV9zTB1sSKCYrCGgMv0_Q

These recoveries have authentication checks removed allowing you to flash any firmware.

Flash both recoveries via fastboot:

fastboot flash recovery FRD_RECOVERY_NoCheck.img
fastboot flash recovery2 FRD_RECOVERY2_NoCheck.img

Reboot your device.

B) PREPARATION / Setting up HiSuite and RedLotus

Download and install HiSuite and nodejs:

HiSuite: consumer.huawei.com/minisite/HiSuite_en/
nodejs: https://nodejs.org/en/download/

Visit RedLotus Github repository and download it (find the green Clone / Download button)

https://github.com/lukx/redlotus

Extract the downloaded file to any directory. Inside that directory, hold down left Shift button and click right mouse button. In the context menu that appears select Open Command Window / Powershell Window here. Do not close this window till the end of the instructions.

Execute the following command inside the CMD / Powershell window.

npm install

You will now download the firmware you want to flash (for example FRD-L09C432B394, only FullOTA-MF supported). Goto TeamMT Firmware Finder and search for the firmware you wish to download. Copy the link to the filelist.xml of that firmware (for example filelist of FRD-L09C432B394: http://update.hicloud.com:8180/TDS/data/files/p3/s15/G1585/g104/v93530/f1/full/filelist.xml)

Execute the following command inside the CMD / Powershell window.

npm run download path-to-firmware-xml (replace last part with actual link)

Wait for the download to complete.

Navigate to C:\Windows\system32\drivers\etc. Open hosts file as Administrator and add this line at the end of it:

127.0.0.1 query.hicloud.com

This will set up a redirection resolving all hicloud queries to your localhost server.

Execute the following command inside the CMD / Powershell window:

npm run listen-hisuite

C) INSTALLATION

Connect the device to computer and ensure that HiSuite is recognizing the attached device. If it isn't go to Settings -> Developer Options and ensure ADB Debugging is enabled.

Hit the Update button in HiSuite. You'll see a message reading a new update is available and the update will be named RedLotus-OTA.

Start the update process and wait patiently.

Your device will eventually reboot to stock recovery and update will start installing. The update might seem to stuck at some percentage. It's normal, wait patiently for the update to install.

You're now updated to the firmware you chose.

OPTIONAL: In case of bootloops, factory reset the device and also unlock bootloader if the device automatically relocked.

Method 2 Using Root

A) PREPARATION / Downloading the required files

Download the modified (NoCheck, authentication removed) stock recovery:

Recovery 1: https://drive.google.com/open?id=0B4SPRmBNsTefSWZLSWxpWGd6QkE
Recovery 2: https://drive.google.com/open?id=0B4SPRmBNsTefSVhxMWFoa01wams

These recoveries have authentication checks removed allowing you to flash any firmware. Move both recovery files to internal storage or any path of your choice (this guide will assume you copied both files to /sdcard)

You will now download the firmware you want to flash (for example FRD-L09C432B394, only FullOTA-MF supported). Goto TeamMT Firmware Finder and search for the firmware you wish to download. Open the filelist.xml of that firmware and download all the files mentioned inside it. For example, the links for FRD-L09C432B394 are

http://update.hicloud.com:8180/TDS/data/files/p3/s15/G1585/g104/v93530/f1/full/update.zip
http://update.hicloud.com:8180/TDS/data/files/p3/s15/G1585/g104/v93530/f1/full/public/update_data_full_public.zip
http://update.hicloud.com:8180/TDS/data/files/p3/s15/G1585/g104/v93530/f1/full/FRD-L09_hw_eu/update_full_FRD-L09_hw_eu.zip

Copy the firmware files to /sdcard/HWOTA (ensure the files are inside HWOTA, it doesn't matters whether you copied the files to internal or external).

B) PREPARATION / Device

Flash the downloaded recoveries via fastboot:

fastboot flash recovery FRD_RECOVERY_NoCheck.img
fastboot flash recovery2 FRD_RECOVERY2_NoCheck.img

Reboot your device.

B) INSTALLATION

After your device is rebooted back to system, open any file manager that supports root.

Navigate to /data/ and create a new folder update/HWOTA.

Copy all the three downloaded zips to the folder created above.

Now using either Terminal Emulator or ADB Shell, grant SU privileges by executing su within the app or shell and further execute the following commands:

echo "--update_package=/data/update/HWOTA/update.zip" > /cache/recovery/command
echo "--update_package=/data/update/HWOTA/update_data_full_public.zip" >> /cache/recovery/command
echo "--update_package=/data/update/HWOTA/update_full_FRD-L09_hw_eu.zip" >> /cache/recovery/command

You need to replace the file names (of the zip files) with the ones you've downloaded.

With everything done reboot your device to recovery:

reboot recovery

OPTIONAL: In case of bootloops, factory reset the device and also unlock bootloader if the device automatically relocked.

Credits:

@mankindtw : he originally patched the Mate 9 recovery removing the authentication. I patched Honor 8 recovery by identifying his edits and adding them.

@OldDroid : for hinting about how to patch the image and because this guide is inspired by his similar guide in Honor 8 Pro forums.