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As he is an EEA national, he can visit and work in Norway for up to 90 days. If he needs to stay longer, he must make an online advance application on the relevant grounds (presumably as a self-employed "service provider") and then present himself at a local Norwegian police station to register. He must take with him his passport, evidence of his self-employment and the contract he is in Norway to complete. It is in the police's sole discretion to issue a registration certificate and there are no rights of appeal, although the application can be made again. If the certificate is issued, it is usually done so quickly (i.e. as a counter service).
The certificate is indefinite (as long as the conditions continue to be met) but will lapse if he leaves Norway for longer than six months.
There is a very useful guidance note provided by the UDI (the Direcotrate of Immigration) which can be found here: http://www.udi.no/Global/UPLOAD/Publikasjoner/FaktaArk/Faktaark_registreringsordningen_en.pdf
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