Oomnitza requires AWS Auth based authentication in the form of an Access Key Id and Secret Access Key. In order to get these credentials, you need to log in to your AWS management console and navigate to Identity and Access Management (IAM). Within the list of users, you can navigate to the user detail screen and access the Security credentials tab which enables you to create a new access key. Once created, these are the values that you will use to create the credential within Oomnitza.
For the integration user on the Oomnitza side, we typically recommend creating a separate user for each type of integration, for example, create a new user called "Amazon Service User" rather than referencing an existing named user.