There are some caveats with using your iPad with your various services you want to secure. Generally, it will depend on if your iPad has a lightning or USB-C connection, and which security protocols the service you are using supports. We'll dive into more details below!
Do YubiKeys work with iPads (with lightning ports)?
For iPads with a lightning port, the YubiKey 5Ci will work with everything the iPhone does. The YubiKey 5Ci will work with the Yubico authenticator app. This is our only key with a direct lightning connection.
Please keep in mind that you cannot use a lightning adapter as the lightning is MFI (made for iPhone) and therefore it may not work. Adapters should work with OTP and FIDO U2F security protocols, however we don’t recommend it.
Do YubiKeys work with iPad Pros (with USB-C)?
When connecting a YubiKey to your iPad Pro over USB-C, the functions that will work are button-press OTP (namely, Yubico OTP or ccccccukedtgvcjbeblfjdeeneidnf
If you have an iPad Pro, please note that our YubiKeys are not compatible with the Yubico Authenticator app (OATH security protocol) because the iPad Pro does not have lightning or NFC capabilities. This is due to Apple's restrictions on what is able to communicate with iPadOS over USB-C, combined with the fact that Apple's MFi program (which we were able to use to enable this kind of communication over the lightning connector) does not apply to the USB-C connector.
In summary: You should be able to use your key with any services that use Yubico OTP on an iPad over USB-C. For services that use WebAuthn, FIDO U2F, and FIDO2, the capability is there in iPadOS if you use the Safari browser (this leverages iPadOS' native support for WebAuthn), but note that some services may simply not give you the option to use a YubiKey if they detect you are logging in from an iPad. This is outside of our control.
For services that support our products via authenticator apps, you should still be able to use Yubico Authenticator with a YubiKey to generate the one-time passwords, but you will not be able to do this on your iPad. You will however be able to generate the OTPs on another device, and then hand-copy them onto your iPad.
You can see which security protocols a service supports in our Works with YubiKey Catalog.
Please see here for further information regarding use of YubiKeys with iPads.