created a custom connector to call a API using oauth: received 403 as response.

Hey, aykhandelwal ,

of course, allow me to citate my blog where I covered this:
https://www.vojtechsima.com/post/api-authentication-in-power-query

let
    // Build the request body as a record with necessary parameters for the token request
    requestBodyQuery = [
        grant_type = "<grant_type>", 
        // The type of grant being requested (e.g., client_credentials)

        client_id = "<client_id>",
        // Your application's client ID

        client_secret = "<client_secret>", 
        // Your application's client secret

        scope = "<scope>"                   
        // The scope of access you're requesting
    ],
    
    // Convert the request body to a URL-encoded string required for the POST request
    requestBodyContent = Text.ToBinary(Uri.BuildQueryString(requestBodyQuery)),
    
    // Make the HTTP POST request to the token endpoint
    request = Json.Document(
        Web.Contents(
            "url", // Replace with the base URL of the token endpoint
            [
                RelativePath = "relativePath", // Replace with the specific path for the token endpoint
                Headers = [
                    #"Content-Type" = "application/x-www-form-urlencoded" // Specify the content type for URL-encoded data
                ],
                Content = requestBodyContent // Include the URL-encoded body in the request
            ]
        )
    ),
    
    accessToken = request[access_token] // Retrieves the "access_token" field from the JSON response
in
    accessToken

This is a template for your OAuth2, once you retrieve the Bearer token, you can do this:

let
    request = Json.Document(
        Web.Contents(
            "url",
            [
                RelativePath = "relativePath",
                Headers = [
                    Authorization = "Bearer acess_token"
                ]
            ]
        )
    )
in
    request

In your case it can look like this:

let
    request = Json.Document(
        Web.Contents(
            "https://onefleetapi.azurewebsites.net",
            [
                RelativePath = "api/v2/labs",
                Headers = [
                    Authorization = "Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsIng1dCI6InlFVXdtW....",
                    Accept = "application/json"
                ]
            ]
        )
    )
in
    request

you changed the manuaal Bearer Token to the response from OAtuh2 access token field.

I tried to follow the above, i haven't used the client secret tough since i am using the Microsoft's official Power BI client ID that's pre-registered in Azure AD.

rest everything is almost same. and added above the response received from the API call.