This might not be what you are looking for, but certainly qualifies as a way to use IAM as a authentication “method” for PAM:
Denis Mikhalkin's (denismo) aws-iam-ldap-bridge periodically populates the LDAP directory location with the users, groups and roles from AWS IAM, which will in turn allow to use libpam-ldap or libpam-ldapd and thereby implicitly authentication of the Linux users against AWS IAM using their AWS IAM Secret Keys as passwords.
Please note the following rather significant caveats:
- At the moment, the plugin requires a custom version of ApacheDS so manual configuration is unlikely - see Configuring an existing ApacheDS LDAP server
- The default configuration is INSECURE however you are free to alter it to your requirements - see Security notes
Personal Assessment
While a native IAM PAM integration would be great (and also enable advanced use cases like AWS Multi-Factor Authentication (MFA)), I like the pragmatic approach to just facilitate the widely used LDAP integration instead - still I would definitely prefer a solution that ideally works with any compliant LDAP server, or at least with a stock ApacheDS distribution, in order to ease installation, maintainability and security assessments.