added script to demonstrate how to use message start events w/ burnettk

spiffworkflow-backend/bin/run_message_start_event_with_api

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+
+function error_handler() {
+  >&2 echo "Exited with BAD EXIT CODE '${2}' in ${0} script at line: ${1}."
+  exit "$2"
+}
+trap 'error_handler ${LINENO} $?' ERR
+set -o errtrace -o errexit -o nounset -o pipefail
+
+script_dir="$( cd -- "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"
+
+if [[ -z "${KEYCLOAK_BASE_URL:-}" ]]; then
+  # export KEYCLOAK_BASE_URL=https://keycloak.dev.spiffworkflow.org
+  export KEYCLOAK_BASE_URL=http://localhost:7002
+fi
+if [[ -z "${BACKEND_BASE_URL:-}" ]]; then
+  # export BACKEND_BASE_URL=https://api.dev.spiffworkflow.org
+  export BACKEND_BASE_URL=http://localhost:7000
+fi
+
+message_identifier="${1:-start_test}"
+username="${2:-admin}"
+password="${3:-admin}"
+realm_name="${4:-spiffworkflow}"
+if [[ -z "${message_identifier}" ]]; then
+  >&2 echo "usage: $(basename "$0") [message_identifier] [username: OPTONAL] [password: OPTONAL] [realm_name: OPTONAL]"
+  exit 1
+fi
+
+function check_result_for_error() {
+  local result="$1"
+  error_code=$(jq '.error_code' <<<"$result")
+  if [[ -n "$error_code" && "$error_code" != "null" ]]; then
+    >&2 echo "ERROR: Failed to run process instance. Received error: $result"
+    exit 1
+  fi
+}
+
+access_token=$("${script_dir}/get_token" "$username" "$password" "$realm_name")
+curl --silent -X POST "${BACKEND_BASE_URL}/v1.0/login_with_access_token?access_token=${access_token}" -H "Authorization: Bearer $access_token" >/dev/null
+result=$(curl --silent -X POST "${BACKEND_BASE_URL}/v1.0/messages/${message_identifier}" -H "Authorization: Bearer $access_token" -d '{"payload": {"email": "HEY@example.com"}}' -H 'Content-type: application/json')
+check_result_for_error "$result"
+echo "$result"

spiffworkflow-backend/src/spiffworkflow_backend/routes/messages_controller.py

@@ -69,7 +69,6 @@ def message_send(
     message_name: str,
     body: Dict[str, Any],
 ) -> flask.wrappers.Response:
-    """Message_start."""
     if "payload" not in body:
         raise (
             ApiError(