Despite being beneficial in automated provisioning of computing infrastructure at scale, infrastructure as code (IaC) scripts are susceptible to containing secrets, such as hard-coded passwords. A derivation of practices related to secret management for IaC can help practitioners to secure their secrets, potentially aiding them to securely develop IaC scripts. The goal of the paper is to help practitioners in secure development of infrastructure as code (IaC) scripts by identifying practices for secret management in IaC. We conduct a grey literature review with 38 Internet artifacts to identify 12 practices. We identify practices that are applicable for all IaC languages, e.g., prioritized encryption, as well as language-specific practices, such as state separation for Terraform states. Our findings can be beneficial for (i) practitioners who can apply the identified practices to secure secrets in IaC development, and (ii) researchers who can investigate how the secret management process can be improved to facilitate secure development of IaC scripts.