[OnePlus 5T  ROMs, Kernels, Recoveries, & Other Dev] j10hx40r:
@quagsirus @qsnc This patch seems to sign the images as before.

$ repo forall device/oneplus/msm8998-common/ -c git diff HEAD
diff --git a/BoardConfigCommon.mk b/BoardConfigCommon.mk
index 11373c6..86a9782 100644
--- a/BoardConfigCommon.mk
+++ b/BoardConfigCommon.mk
@@ -44,6 +44,9 @@ BOARD_KERNEL_IMAGE_NAME := Image.gz-dtb
TARGET_KERNEL_SOURCE := kernel/oneplus/msm8998
TARGET_KERNEL_CONFIG := lineage_oneplus5_defconfig

+# Boot image signing
+BOARD_CUSTOM_BOOTIMG_MK=$(PLATFORM_PATH)/mkbootimg.mk
+
# QCOM hardware
BOARD_USES_QCOM_HARDWARE := true

diff --git a/mkbootimg.mk b/mkbootimg.mk
new file mode 100644
index 0000000..fa49f42
--- /dev/null
+++ b/mkbootimg.mk
@@ -0,0 +1,36 @@
+BOOT_SIGNER := $(HOST_OUT_EXECUTABLES)/boot_signer
+BOOT_IMAGE_SIGNING_KEY := build/make/target/product/security/testkey
+
+recoveryimage-deps += $(BOOT_SIGNER)
+
+# $1: boot image target
+define build_boot_supports_boot_signer
+ $(MKBOOTIMG) --kernel $(call bootimage-to-kernel,$(1)) $(INTERNAL_BOOTIMAGE_ARGS) $(INTERNAL_MKBOOTIMG_VERSION_ARGS) $(BOARD_MKBOOTIMG_ARGS) --output $(1)
+ $(BOOT_SIGNER) /boot $@ $(BOOT_IMAGE_SIGNING_KEY).pk8 $(BOOT_IMAGE_SIGNING_KEY).x509.pem $(1)
+ $(call assert-max-image-size,$(1),$(call get-bootimage-partition-size,$(1),boot))
+endef
+
+$(INSTALLED_BOOTIMAGE_TARGET): $(MKBOOTIMG) $(INTERNAL_BOOTIMAGE_FILES) $(BOOT_SIGNER)
+ $(call pretty,"Target boot image: $@")
+ $(call build_boot_supports_boot_signer,$@)
+
+$(call declare-1p-container,$(INSTALLED_BOOTIMAGE_TARGET),)
+$(call declare-container-license-deps,$(INSTALLED_BOOTIMAGE_TARGET),$(INTERNAL_BOOTIMAGE_FILES),$(PRODUCT_OUT)/:/)
+
+UNMOUNTED_NOTICE_DEPS += $(INSTALLED_BOOTIMAGE_TARGET)
+
+.PHONY: bootimage-nodeps
+bootimage-nodeps: $(MKBOOTIMG) $(BOOT_SIGNER)
+ @echo "make $@: ignoring dependencies"
+ $(foreach b,$(INSTALLED_BOOTIMAGE_TARGET),$(call build_boot_supports_boot_signer,$(b)))
+
+# $(1): output file
+define build-recoveryimage-target
+ $(MKBOOTIMG) $(INTERNAL_RECOVERYIMAGE_ARGS) $(INTERNAL_MKBOOTIMG_VERSION_ARGS) $(BOARD_RECOVERY_MKBOOTIMG_ARGS) --output $(1)
+ $(BOOT_SIGNER) /recovery $(1) $(BOOT_IMAGE_SIGNING_KEY).pk8 $(BOOT_IMAGE_SIGNING_KEY).x509.pem $(1)
+ $(call assert-max-image-size,$(1),$(call get-hash-image-max-size,$(BOARD_RECOVERYIMAGE_PARTITION_SIZE)))
+endef
+
+$(INSTALLED_RECOVERYIMAGE_TARGET): $(recoveryimage-deps)
+ $(call build-recoveryimage-target, $@)
+

Here is the binwalk of resultant boot and recovery image

$ binwalk out/target/product/dumpling/boot.img

DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
0 0x0 Android bootimg, kernel size: 15985080 bytes, kernel addr: 0x8000, ramdisk size: 1454967 bytes, ramdisk addr: 0x1000000, product name: ""
4096 0x1000 gzip compressed data, maximum compression, from Unix, last modified: 1970-01-01 00:00:00 (null date)
12588113 0xC01451 Flattened device tree, size: 422985 bytes, version: 17
12970593 0xC5EA61 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
13011098 0xC6889A Flattened device tree, size: 427295 bytes, version: 17
13397290 0xCC6D2A Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
13438393 0xCD0DB9 Flattened device tree, size: 427295 bytes, version: 17
13824585 0xD2F249 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
13865688 0xD392D8 Flattened device tree, size: 422928 bytes, version: 17
14248120 0xD968B8 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
14288616 0xDA06E8 Flattened device tree, size: 422985 bytes, version: 17
14671096 0xDFDCF8 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
14711601 0xE07B31 Flattened device tree, size: 427295 bytes, version: 17
15097793 0xE65FC1 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
15138896 0xE70050 Flattened device tree, size: 427295 bytes, version: 17
15525088 0xECE4E0 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
15566191 0xED856F Flattened device tree, size: 422985 bytes, version: 17
15948671 0xF35B7F Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
15990784 0xF40000 gzip compressed data, from Unix, last modified: 1970-01-01 00:00:00 (null date)
17448967 0x10A4007 Certificate in DER format (x509 v3), header length: 4, sequence length: 1192

$ binwalk out/target/product/dumpling/recovery.img

DECIMAL HEXADECIMAL DESCRIPTION
--------------------------------------------------------------------------------
0 0x0 Android bootimg, kernel size: 15985080 bytes, kernel addr: 0x8000, ramdisk size: 12170245 bytes, ramdisk addr: 0x1000000, product name: ""
4096 0x1000 gzip compressed data, maximum compression, from Unix, last modified: 1970-01-01 00:00:00 (null date)
12588113 0xC01451 Flattened device tree, size: 422985 bytes, version: 17
12970593 0xC5EA61 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
13011098 0xC6889A Flattened device tree, size: 427295 bytes, version: 17
13397290 0xCC6D2A Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
13438393 0xCD0DB9 Flattened device tree, size: 427295 bytes, version: 17
13824585 0xD2F249 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
13865688 0xD392D8 Flattened device tree, size: 422928 bytes, version: 17
14248120 0xD968B8 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
14288616 0xDA06E8 Flattened device tree, size: 422985 bytes, version: 17
14671096 0xDFDCF8 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
14711601 0xE07B31 Flattened device tree, size: 427295 bytes, version: 17
15097793 0xE65FC1 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
15138896 0xE70050 Flattened device tree, size: 427295 bytes, version: 17
15525088 0xECE4E0 Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
15566191 0xED856F Flattened device tree, size: 422985 bytes, version: 17
15948671 0xF35B7F Unix path: /dev/block/platform/soc/1da4000.ufshc/by-name/vendor
15990784 0xF40000 gzip compressed data, from Unix, last modified: 1970-01-01 00:00:00 (null date)
28164103 0x1ADC007 Certificate in DER format (x509 v3), header length: 4, sequence length: 1192

I still need to do on device testing. As I use my oneplus 5t as my daily driver, I am bit unwilling to lose the data for the same. Does any one want to volunteer for the testing?