Your requirements could not be resolved to an installable set of packages.
Problem 1
- Root composer.json requires simplesamlphp/simplesamlphp ^2.4, found simplesamlphp/simplesamlphp[dev-feature/symfony-forms, ..., dev-bilateral_attrs, v1.12.0, ..., 1.19.9, v2.0.0-beta.1, ..., v2.3.2, 3.0.x-dev (alias of dev-master)] but it does not match the constraint.