I have resolved the issue:

You need to create the password by specifying the realm as follows:

htdigest -c .htpasswd realmyouwanttoset username_setted 
Enter password: pwfantasy 
Retype password: pwfantasy 

Then, you can set the arguments as shown below:

SWUPDATE_WEBSERVER_ARGS=" -r /srv/swupdate/mongoose-webapp -p 8081 --auth-domain realmyouwanttoset --global-auth-file /whereyourfileis/.htpasswd " 

Basic authentication configured successfully. 📈📈