How to interact with html response from http request in Flutter - flutter

Question

I have a Flutter app where I am running a Google Apps Script through an http request. The purpose of the script is to create a Form and link the responses to a spreadsheetID that is passed in. The script is configured to only allow Google accounts access it and I've set up the flutter app to use a Service Account to access the script using the format:
getCredentials().then( (AuthClient client){
response = client.get(url, headers{"Authorization": "Bearer ${client.access_token}");
});
Issue: The issue is that the first time that the Service Account makes a request it will get an HTML response saying that it the account needs to give permission to the script to access its data and I'm not sure how to do that.
I'm fairly new to making http requests and using it with the GoogleAPI so I'm stuck. Any advice?

Answer 1

Goal
Create a web page which anyone can use to submit a Google sheet link and for the app to create a form and link the sheet to that.
Authorization
For this users will require a google account and they will be required to go through the OAuth process to authorize your app.
To create the form and link it from client-side JavaScript you would indeed need to call the Apps Script API, though you cannot do this with a service account.
From: https://developers.google.com/apps-script/api/how-tos/execute
Warning: The Apps Script API doesn't work with service accounts.
Luckily, you don't need a service account to do this.
Instructions
Create an Apps Script project with a function something like:
function createForm(ssID){
form = FormApp.create("Your New Form");
form.setDestination(FormApp.DestinationType.SPREADSHEET, ssID);
let formLink = form.getPublishedUrl();
return formLink;
}
Save and take a note of the ID of the script project.
Set up a GCP project (sounds like you already have one).
Make sure the Apps Script API is enabled in your GCP.
Configure the OAuth consent screen and add the scope - https://www.googleapis.com/auth/forms.
Create an API key and a Client ID - add http://localhost:8000 or whatever port you are testing on to the "Authorized JavaScript Origins"
Create OAuth credentials "web browser (JavaScript)".
Link your Apps Script project to the same GCP project - Instructions
Deploy the Apps Script project as an API executable - take not of the deployment ID, although the documentation says that you need the script ID, it is wrong, at least with the new Apps Script IDE.
Write the client-side JavaScript in your app like what is found in the quickstart. Which will enable users to authorize the app. You need to add in the scopes and keys there too. I recommend just following the quick start steps first to get a feel for it. You can use the authorization parts without modification.
Then add in the function that will call your Apps Script, something like this:
function appsScriptCreateForm(ssId) {
var scriptId = "<DEPLOYMENT_ID>";
// Run your Apps Script function
gapi.client.script.scripts
.run({
scriptId: scriptId,
resource: {
function: "createForm",
parameters: [ssId],
},
})
.then(function (resp) {
var result = resp.result;
// ERROR HANDLING
if (result.error && result.error.status) {
appendPre("Error calling API:");
appendPre(JSON.stringify(result, null, 2));
} else if (result.error) {
var error = result.error.details[0];
appendPre("Script error message: " + error.errorMessage);
if (error.scriptStackTraceElements) {
appendPre("Script error stacktrace:");
for (var i = 0; i < error.scriptStackTraceElements.length; i++) {
var trace = error.scriptStackTraceElements[i];
appendPre("\t" + trace.function + ":" + trace.lineNumber);
}
}
// IF SUCCESSFUL
} else {
console.log("success", resp);
}
});
}
Write your HTML with the buttons and inputs necessary.
Add event listeners where appropriate.
Profit!
Please note
This set up is your project running with the authorization of other accounts.
The API requests count against your quota.
You can see details of all the executions in your GCP Project Dashboard.
Users require a Google account and need to authorize the app.
In the Apps Script function above, you just need to pass in the Spreadsheet ID. Not the whole link. You could ask for the whole link and then use Regex to extract the ID if you wanted.
This can be quite tricky and easy to miss a step or make a mistake, so double check your work.
If, after successful authorization, when trying to run the script you get a 404 error, the request has been built wrong, check your IDs. If you get a 500 error, that can mean that the Apps Script function has successfully been called, but, there was an error within Apps Script and failed, check the executions page of the Apps Script editor.
References
Apps Script How to Execute
Apps Script JS Quickstart - Highly recommended you follow these steps first and get that working!
How to link your Apps Script to GCP