fix: contain entire auth header in ProviderConfig

[mariatsji]

Will require a secret configured like so

export basicauth="Bearer $(echo "myuser_mykey" | base64)"
kubectl create secret -n my-namespace generic my-secret --from-literal basicauth="$basicauth"

[tenstad]

When converting to a string at the end I think we might as well do it early instead

[mariatsji]

When converting to a string at the end I think we might as well do it early instead
agreed - fixed