setting up docker build workflow

6/Program.cs

@@ -1,13 +1,13 @@
 using Example.Data;
 using Microsoft.AspNetCore.Identity;
 using Microsoft.EntityFrameworkCore;
+using Npgsql;
 
 var builder = WebApplication.CreateBuilder(args);
 
-var connectionString = builder.Configuration.GetConnectionString("DefaultConnection")
-    ?? throw new InvalidOperationException("Connection string 'DefaultConnection' was not found.");
 var configuredProvider = builder.Configuration["Database:Provider"]
     ?? throw new InvalidOperationException("Database provider configuration 'Database:Provider' was not found.");
+var connectionString = ResolveConnectionString(builder, configuredProvider);
 
 if (builder.Environment.IsDevelopment())
 {
@@ -116,3 +116,42 @@ static void ValidateConnectionString(string connectionString, string configuredP
 
     throw new InvalidOperationException($"Unsupported database provider '{configuredProvider}'.");
 }
+
+static string ResolveConnectionString(WebApplicationBuilder builder, string configuredProvider)
+{
+    var configuredConnectionString = builder.Configuration.GetConnectionString("DefaultConnection")
+        ?? throw new InvalidOperationException("Connection string 'DefaultConnection' was not found.");
+
+    if (builder.Environment.IsDevelopment() ||
+        !string.Equals(configuredProvider, "Postgres", StringComparison.OrdinalIgnoreCase))
+    {
+        return configuredConnectionString;
+    }
+
+    var passwordFile = builder.Configuration["POSTGRES_PASSWORD_FILE"];
+    if (string.IsNullOrWhiteSpace(passwordFile) || !File.Exists(passwordFile))
+    {
+        return configuredConnectionString;
+    }
+
+    var password = File.ReadAllText(passwordFile).Trim();
+    if (string.IsNullOrWhiteSpace(password))
+    {
+        throw new InvalidOperationException($"The PostgreSQL password file '{passwordFile}' is empty.");
+    }
+
+    var connectionStringBuilder = new NpgsqlConnectionStringBuilder(configuredConnectionString)
+    {
+        Host = builder.Configuration["POSTGRES_HOST"] ?? "db",
+        Database = builder.Configuration["POSTGRES_DB"] ?? "db",
+        Username = builder.Configuration["POSTGRES_USER"] ?? "user",
+        Password = password
+    };
+
+    if (int.TryParse(builder.Configuration["POSTGRES_PORT"], out var port))
+    {
+        connectionStringBuilder.Port = port;
+    }
+
+    return connectionStringBuilder.ConnectionString;
+}