How to load a data in Multi-Page App based on requests header?

Dash Python
1

Hello,

In the request header, I will have stored information about the given user. And based on the user name, I would love to load data from the SQL server. I only know how to do that inside callback functions like update graph()

@app.callback(
    Output(component_id="pie-chart", component_property="figure"),
    [Input(component_id="dropdown", component_property="value"),
     Input(component_id="url", component_property='href'), ],
    prevent_initial_call=False,
)
def update_graph(name, href):
    headers = flask.request.headers
    print(headers)
    kpi = load_data(user=headers['token'])
    kpi = kpi[kpi["Level"].isin(name)]
    fig = px.pie(kpi, names="Level", values="Count")
    return fig

Can I somehow achieve the same but before callback? I mean if I Have app1.py file with the structure:

# app1.py 


headers = flask.request.headers  # here I get an error because at this stage flask server doesn't run yet. 
kpi = load_data(user=headers['token'])

layout = [...]

@app.callback(
    Output(component_id="pie-chart", component_property="figure"),
    [Input(component_id="dropdown", component_property="value"),
     Input(component_id="url", component_property='href'), ],
    prevent_initial_call=False,
)
def update_graph(name, href):
    kpi = kpi[kpi["Level"].isin(name)]
    fig = px.pie(kpi, names="Level", values="Count")
    return fig

Do you have any ideas on how to achieve my goal? Or can I load data only inside callback (if yes how then I can create dropdowns for layout if at layout createtion stage I don’t know yet options, values for dropdown)?