Log into the Azure Portal here then search for and click on 'App registration', then 'New registration'.
To register the application, give it a name such as 'Reading Cloud Azure SSO' and in the 'Supported account types' section, select 'Accounts in this organization directory only (Default Directory only - Single tenant)'
Keep this page open and in another tab on your browser, load the library system. Navigate to the Identifier providers section and select 'Azure AD'. Under Redirection Settings, click the 'Copy' button to copy the redirect URL to your clipboard. Now return to the previous page and under 'Redirect URI, select 'Web' and then paste the link you just copied into the box.
Click 'Register' and you will be presented with a list of IDs.
Copy the Application (client) ID and in another window, ensure you have selected your identity provider and paste it into the relevant box. Repeat the process for the Directory (tenant) ID.