docker build cannot find file secret file outside home directory

Question

I'm building a docker image as follows:

TEMP_FILE="/home/username/any/directory/temp"
touch $TEMP_FILE

<secrets> > $TEMP_FILE

export DOCKER_BUILDKIT=1
pushd $PROJECT_ROOT
  docker build -t $DOCKER_IMAGE_NAME \
               --secret id=netrc,src=$TEMP_FILE \
               --build-arg=<...> \
               -f Dockerfile .
  rm $TEMP_FILE

Currently this works.

I'd now like to use $(mktemp) to create the TEMP_FILE in the /tmp directory. However, when I point TEMP_FILE outside of /home, I get the following error:

could not parse secrets: [id=netrc,src=/tmp/temp-file-name]: failed to stat /tmp/temp-file-name: stat /tmp/temp-file-name: no such file or directory

The script itself has no issue, I can easily find and view the temporary file for example with cat $TEMP_FILE.

How do I give docker build access to /tmp?