I've successfully connected to SharePoint Online using PHP. It looks to me like you're combining two different methods to do so. Here is what I did:

• Register my app in Azure AD on the Management Portal to get client_id, client_secret, redirectUri and the right permissions on Office 365 for sites.
• Call the authorization endpoint at https://login.windows.net/common/oauth2/authorize
• Call the token service endpoint at https://login.windows.net/common/oauth2/token
• Call the SharePoint REST endpoint with the access token.
• The resource should be simply the URL of your SharePoint site.

The appregnew.aspx and appprincipals.aspx pages are used for apps for SharePoint but it doesn't look like you're building one.

I've successfully connected to SharePoint Online using PHP. It looks to me like you're combining two different methods to do so. Here is what I did:

• Register my app in Azure AD on the Management Portal to get client_id, client_secret, redirectUri and the right permissions on Office 365 for sites.
• Call the authorization endpoint at https://login.microsoftonline.com/common/oauth2/authorize
• Call the token service endpoint at https://login.microsoftonline.com/common/oauth2/token
• Call the SharePoint REST endpoint with the access token.
• The resource should be simply the URL of your SharePoint site.

The appregnew.aspx and appprincipals.aspx pages are used for apps for SharePoint but it doesn't look like you're building one.