in src/main/java/org/apache/sling/auth/oauth_client/impl/OAuthEntryPointServlet.java [101:114]
private RedirectTarget getAuthenticationRequestUri(ClientConnection connection, SlingHttpServletRequest request, URI redirectUri) {
ResolvedOAuthConnection conn = ResolvedOAuthConnection.resolve(connection);
// The client ID provisioned by the OpenID provider when
// the client was registered
ClientID clientID = new ClientID(conn.clientId());
String redirect = request.getParameter(OAuthStateManager.PARAMETER_NAME_REDIRECT);
String perRequestKey = new Identifier().getValue();
State state = stateManager.toNimbusState(new OAuthState(perRequestKey, connection.name(), redirect));
return RedirectHelper.buildRedirectTarget(clientID, conn.authorizationEndpoint(), conn.scopes(), conn.additionalAuthorizationParameters(), state, perRequestKey, redirectUri);
}