First, you need to have access to the Strava API. Register for a Strava developer account by visiting the Strava Developers website. Create an application to obtain your Client ID and Client Secret, which you'll use for API authentication.

Strava uses OAuth for user authentication. Direct the user to Strava's authorization page using the URL with your Client ID, redirect URI, and requested scopes. Once the user authorizes, they'll be redirected to your specified URI with a code parameter. Use this code to request an access token by making a POST request to the Strava token exchange endpoint.

With the access token, you can now make API requests to Strava. Use the token to authenticate requests to endpoints such as `/athlete/activities` to fetch activities data. Use an HTTP library like `requests` in Python to send these GET requests.

Strava API responses are in JSON format. Parse the JSON data retrieved from the API using a JSON library in your programming language of choice (e.g., `json` module in Python). Extract the desired data fields you want to save.

Organize and structure the extracted data into a Python dictionary (or similar structure in another language) that aligns with how you want your JSON file to be formatted. Ensure only the relevant data is included.

Use a JSON library to write the structured data to a JSON file. In Python, you can use the `json.dump()` function, specifying your dictionary and the file path. This saves the data in a human-readable JSON format.

Open the JSON file to verify that the data is correctly formatted and complete. Ensure that sensitive information, like access tokens, are not stored in the JSON file. For security, store tokens in environment variables or secure vaults, not in code or configuration files.

By following these steps, you can efficiently move data from Strava to a JSON file without relying on third-party connectors or integrations.