Because it is easy to extract strings from an application source code or binary, credentials should not be hard-coded. This is particularly true
for applications that are distributed or that are open-source.
In the past, it has led to the following vulnerabilities:
Credentials should be stored outside of the code in a configuration file, a database, or a management service for secrets.
This rule flags instances of hard-coded credentials used in database and LDAP connections. It looks for hard-coded credentials in connection
strings, and for variable names that match any of the patterns from the provided list.
Ask Yourself Whether
  -  Credentials allow access to a sensitive component like a database, a file storage, an API or a service. 
-  Credentials are used in production environments. 
-  Application re-distribution is required before updating the credentials. 
There is a risk if you answered yes to any of those questions.
Recommended Secure Coding Practices
  -  Store the credentials in a configuration file that is not pushed to the code repository. 
-  Store the credentials in a database. 
-  Use your cloud provider’s service for managing secrets. 
-  If a password has been disclosed through the source code: change it. 
Sensitive Code Example
username = 'admin'
password = 'admin' # Sensitive
usernamePassword = 'user=admin&password=admin' # Sensitive
Compliant Solution
import os
username = os.getenv("username") # Compliant
password = os.getenv("password") # Compliant
usernamePassword = 'user=%s&password=%s' % (username, password) # Compliant{code}
See