Fix spelling errors reported by lintian

[ellert]

• authentification → authentication
• converstion → conversion
• occured → occurred
• reponse → response
• unknow → unknown

[mpatrascoiu]

Hello Mattias,

Thank you for the Pull Request! I feel almost a bit nostalgic to see authentification go.

Cheers,
Mihai

[andrea-manzi]

https://en.wiktionary.org/wiki/authentification :zipper_mouth_face: