Microsoft Graph API - AuthenticationError when accessing mail - rest

Question

I'm currently implementing an Outlook Add-In that should access certain mail fields. So I setup a starter project and set the delegated Mail.Read permission in the Microsoft Azure Active Directory settings and added it to my scope configuration.
However, when I send the request for
graph.microsoft.com/v1.0/me/messages/
I get this as a response:
Error: Bad Request
at IncomingMessage.<anonymous> (C:\Users\zz\public\javascripts\odata-helper.js:53:29)
at IncomingMessage.emit (events.js:322:22)
at endReadableNT (_stream_readable.js:1187:12)
at processTicksAndRejections (internal/process/task_queues.js:84:21) {
code: 400,
bodyCode: 'AuthenticationError',
bodyMessage: 'Error authenticating with resource'
}
I don't understand why this error appears since the user authentication works and I don't have any problems with other Graph Endpoints (e.g. retrieving a list of my OneDrive files from /me/drive/root/children)
I am using this as a codebase:
https://learn.microsoft.com/en-us/office/dev/add-ins/develop/create-sso-office-add-ins-nodejs

Answer 1

I didn't reproduce your issue and graph.microsoft.com/v1.0/me/messages works fine in the sample you shared.
Please refer to my configuration.
In addition to the configuration mentioned in the documentation, I also made the following changes.
Add a Mail.Read Delegated permission in Azure AD app.
Modify the Microsoft Graph endpoint in app.js file. Please note I'm querying the subject property of messages. So I modified the two places: $select=subject&$top=10 and itemNames.push(item['subject']).
app.get('/getuserdata', async function(req, res, next) {
const graphToken = req.get('access_token');
const graphData = await getGraphData(graphToken, "/me/messages", "?$select=subject&$top=10");
if (graphData.code) {
next(createError(graphData.code, "Microsoft Graph error " + JSON.stringify(graphData)));
}
else
{
const itemNames = [];
const oneDriveItems = graphData['value'];
for (let item of oneDriveItems){
itemNames.push(item['subject']);
}
res.send(itemNames)
}
}
In the add-in manifest file "manifest\manifest_local.xml", I add a scope "Mail.Read".
<WebApplicationInfo>
<Id>a7eb1d00-f724-4799-8a46-809f2dba63f8</Id>
<Resource>api://localhost:44355/a7eb1d00-f724-4799-8a46-809f2dba63f8</Resource>
<Scopes>
<Scope>Files.Read.All</Scope>
<Scope>profile</Scope>
<Scope>Mail.Read</Scope>
</Scopes>
</WebApplicationInfo>
In the file routes\authRoute.js, I add the 'Mail.Read' like this:
else {
const [schema, jwt] = authorization.split(' ');
const formParams = {
client_id: process.env.CLIENT_ID,
client_secret: process.env.CLIENT_SECRET,
grant_type: 'urn:ietf:params:oauth:grant-type:jwt-bearer',
assertion: jwt,
requested_token_use: 'on_behalf_of',
scope: ['Files.Read.All', 'Mail.Read'].join(' ')
};
These are all the configurations and I can get the subject of messages in Microsoft Word addin: