Working solution :

location /api/auth/ {
   rewrite ^/api/auth(.*) $1 break;
   proxy_pass http://localhost:8085/;
}

About this regex :

• ^/api/auth(.*) :

due to ^, means every caractere chain begining with /api/auth(.*)

• Where (.*) :

represent a group of any character.

• $1 represent the group of caractere.

Example /api/auth/account/login :

• it begins with /api/auth
• (.*) = /account/login
• so $1 = /account/login