(Objective-C) Refresh Microsoft Teams OAuth2 Access Token

Refreshes a Microsoft Teams OAuth2 access token. When an access token expires, HTTPS requests will receive a 401 status response indicating failure. When that happens, your application can run this code to refresh the access token, and then retry the request using the new access token. Refreshing an access token does not need user interaction (i.e. does not need to display a browser to have the user interactive authorize access).

For more information, see https://docs.microsoft.com/en-us/graph/auth-v2-user?context=graph/api/1.0#5-use-the-refresh-token-to-get-a-new-access-token

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#import <CkoJsonObject.h>
#import <CkoOAuth2.h>
#import <CkoStringBuilder.h>

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// It is assumed we previously obtained an OAuth2 access token.
// This example loads the JSON access token file 
// saved by this example: Get Microsoft Teams OAuth2 Access Token

CkoJsonObject *jsonToken = [[CkoJsonObject alloc] init];
BOOL success = [jsonToken LoadFile: @"qa_data/tokens/microsoft_teams.json"];
if (success != YES) {
    NSLog(@"%@",@"Failed to load APP.json");
    return;
}

// The access token JSON looks like this:

// {
//   "token_type": "Bearer",
//   "scope": "openid profile ...",
//   "expires_in": 3600,
//   "ext_expires_in": 3600,
//   "access_token": "...",
//   "refresh_token": "...",
//   "id_token": "..."
// }

CkoOAuth2 *oauth2 = [[CkoOAuth2 alloc] init];

oauth2.TokenEndpoint = @"https://login.microsoftonline.com/common/oauth2/v2.0/token";

// Replace these with actual values.
oauth2.ClientId = @"MICROSOFT-GRAPH-CLIENT-ID";
// This is your app password:
oauth2.ClientSecret = @"MICROSOFT-GRAPH-CLIENT-SECRET";

// Get the "refresh_token"
oauth2.RefreshToken = [jsonToken StringOf: @"refresh_token"];

// Send the HTTP POST to refresh the access token..
success = [oauth2 RefreshAccessToken];
if (success != YES) {
    NSLog(@"%@",oauth2.LastErrorText);
    return;
}

[jsonToken UpdateString: @"access_token" value: oauth2.AccessToken];
[jsonToken UpdateString: @"refresh_token" value: oauth2.RefreshToken];

// Save the new JSON access token response to a file.
CkoStringBuilder *sbJson = [[CkoStringBuilder alloc] init];
jsonToken.EmitCompact = NO;
[jsonToken EmitSb: sbJson];
[sbJson WriteFile: @"qa_data/tokens/microsoft_teams.json" charset: @"utf-8" emitBom: NO];

NSLog(@"%@",@"OAuth2 token refreshed!");
NSLog(@"%@%@",@"New Access Token = ",oauth2.AccessToken);