Man pages matching name net::oauth::signaturemethod::plaintext in section 3pm:

Net::OAuth::SignatureMethod::PLAINTEXT.3pm.en	debian 10 / libnet-oauth-perl
Net::OAuth::SignatureMethod::PLAINTEXT.3pm.en	debian 11 / libnet-oauth-perl
Net::OAuth::SignatureMethod::PLAINTEXT.3pm.en	debian 12 / libnet-oauth-perl