Getting 401 unauthorised when calling calendar api of office 365 - json

Question

I am trying to access the office 365 calendar api to create an event. The steps i followed are
Created app and registered it in azure
Gave permisissions to the app
Hitting https://login.microsoftonline.com/{{tenantid}}/oauth2/token to get the access token
body :
{
"grant_type":"client_credentials",
"client_id": "*****",
"client_secret": "****",
"resource":"https://outlook.office.com"
}
Response :
{
"token_type": "Bearer",
"expires_in": "3600",
"ext_expires_in": "262800",
"expires_on": "1532026206",
"not_before": "1532022306",
"resource": "https://outlook.office.com",
"access_token":"******"
}
When i pass this access token to https://outlook.office.com/api/v2.0/me/events which creates events. it gives me 401 unauthorised. Body of the request is as shown below. Someone please assist.
{
"Subject": "Discuss the Calendar REST API",
"Body": {
"ContentType": "HTML",
"Content": "I think it will meet our requirements!"
},
"Start": {
"DateTime": "2019-02-02T18:00:00",
"TimeZone": "Pacific Standard Time"
},
"End": {
"DateTime": "2019-02-02T19:00:00",
"TimeZone": "Pacific Standard Time"
},
"Attendees": [
{
"EmailAddress": {
"Address": "arulvelug#hexabot.onmicrosoft.com",
"Name": "Arulvelu G"
},
"Type": "Required"
}
]
}

Answer 1

To do authorization of office 365 and use REST API via Postman, here is a solution for your reference:
First: get security Token
Access [https://login.microsoftonline.com/extSTS.srf] via Http Post method. The content of the http request is as follows.
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"
xmlns:a="http://www.w3.org/2005/08/addressing"
xmlns:u="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-
utility-1.0.xsd">
<s:Header>
<a:Action
s:mustUnderstand="1">http://schemas.xmlsoap.org/ws/2005/02/trust/RST/Issue</a:Action>
<a:ReplyTo>
<a:Address>http://www.w3.org/2005/08/addressing/anonymous</a:Address>
</a:ReplyTo>
<a:To s:mustUnderstand="1">https://login.microsoftonline.com/extSTS.srf</a:To>
<o:Security s:mustUnderstand="1"
xmlns:o="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd">
<o:UsernameToken>
<o:Username>[username]</o:Username>
<o:Password>[password]</o:Password>
</o:UsernameToken>
</o:Security>
</s:Header>
<s:Body>
<t:RequestSecurityToken xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust">
<wsp:AppliesTo xmlns:wsp="http://schemas.xmlsoap.org/ws/2004/09/policy">
<a:EndpointReference>
<a:Address>[endpoint]</a:Address>
</a:EndpointReference>
</wsp:AppliesTo>
<t:KeyType>http://schemas.xmlsoap.org/ws/2005/05/identity/NoProofKey</t:KeyType>
<t:RequestType>http://schemas.xmlsoap.org/ws/2005/02/trust/Issue</t:RequestType>
<t:TokenType>urn:oasis:names:tc:SAML:1.0:assertion</t:TokenType>
</t:RequestSecurityToken>
</s:Body>
</s:Envelope>
The demonstration screenshot in Postman:
And the response content will include a security token as below, we can use this security token to get Access Token of office 365.
Second: get Access Token
Here i show you how to get access token, I get it of my SharePoint using the security token.
Access [https://yourdomain.sharepoint.com/_forms/default.aspx?wa=wsignin1.0] via http Post method. The content of the request is the security token that we have got above as below.
And the response as below:
We can see that there are two cookie, rtFa and FedAuth in response header, and these two cookie need to be added to the request in subsequent request.
Third: get Request Digest
Access [https://yourdomain.sharepoint.com/_api/contextinfo] via http Post method with that two cookies which we have got above.
And the response as below:
This is the final Token we want!
Then we can use REST API of our app in O365, like SharePoint , we only need to add this token and the previous two cookie, as shown in the following figure.