I found this blog https://admin.salesforce.com/blog/2018/the-value-of-having-a-dedicated-salesforce-integration-user by using this we can create an Integration User the user is an remote user(no human is access it) the user can manage the all the integrations related to the organizations.in my integration i want this Integration user credentials instead of typing the username and password of this integration user.I want to fetch this Integration user details by using Rest API can anyone help me is it possible or not.
Your question includes a serious misunderstanding of how integrations authenticate and are secured. Continuing to pursue this line of inquiry instead of learning more about integration security may put your production systems at serious risk. You need to stop and learn before you continue your work.
An integration should never have access to the actual credentials under which it authenticates. However, some legacy integrations do store a username and password and authenticate using SOAP login or the OAuth username-password flow. This is a bad practice. You should never implement a new integration that stores raw credentials.
You cannot retrieve a user's credentials via the REST API as this would be incredibly insecure (and require you to have some other credentials just to talk to the REST API). The direct answer to your question is absolutely not.
All integrations should be authenticated to Salesforce using OAuth. OAuth provides the integration with an access token and optionally a refresh token. The integration can use these tokens to maintain persistent access to the API without storing or retrieving credentials. OAuth authentication using an integration user, a Connected App, and the Web Server or JWT OAuth flow provides your organization with the best security posture, including the ability to use a minimal permissioning model, monitor integration activity, selectively revoke access, and rotate credentials safely.
OAuth is a very large area; you can start learning with this Trailhead module.