Assign output of command to a variable, then use the variable. Needs $<); \
to pipe the output and concatenate the subsequent line, since each line is executed in a separate shell.
# Usage: make db-upgrade-gcp environment=dev
db-upgrade-gcp:
TOKEN=$$(gcloud auth print-identity-token $<); \
python bin/db_upgrade_gcp.py $(environment) --gcp_token $$TOKEN