fix: improve password validation flow (#15132)

Refers to #14984 

Currently, password validation is done backend side and is not explicit
enough so it can be painful to create first users.
We'd like to make this validation easier - but also duplicate it
frontend side to make it smoother.

Flows involved : 
- First user set password
- New user set password
- Change password

---------

Co-authored-by: BrunoQuaresma <bruno_nonato_quaresma@hotmail.com>

coderd/userpassword/userpassword_test.go

@@ -5,6 +5,7 @@
 package userpassword_test
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -12,46 +13,101 @@ import (
 	"github.com/coder/coder/v2/coderd/userpassword"
 )
 
-func TestUserPassword(t *testing.T) {
+func TestUserPasswordValidate(t *testing.T) {
 	t.Parallel()
-	t.Run("Legacy", func(t *testing.T) {
-		t.Parallel()
-		// Ensures legacy v1 passwords function for v2.
-		// This has is manually generated using a print statement from v1 code.
-		equal, err := userpassword.Compare("$pbkdf2-sha256$65535$z8c1p1C2ru9EImBP1I+ZNA$pNjE3Yk0oG0PmJ0Je+y7ENOVlSkn/b0BEqqdKsq6Y97wQBq0xT+lD5bWJpyIKJqQICuPZcEaGDKrXJn8+SIHRg", "tomato")
-		require.NoError(t, err)
-		require.True(t, equal)
-	})
+	tests := []struct {
+		name     string
+		password string
+		wantErr  bool
+	}{
+		{name: "Invalid - Too short password", password: "pass", wantErr: true},
+		{name: "Invalid - Too long password", password: strings.Repeat("a", 65), wantErr: true},
+		{name: "Invalid - easy password", password: "password", wantErr: true},
+		{name: "Ok", password: "PasswordSecured123!", wantErr: false},
+	}
 
-	t.Run("Same", func(t *testing.T) {
-		t.Parallel()
-		hash, err := userpassword.Hash("password")
-		require.NoError(t, err)
-		equal, err := userpassword.Compare(hash, "password")
-		require.NoError(t, err)
-		require.True(t, equal)
-	})
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			err := userpassword.Validate(tt.password)
+			if tt.wantErr {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}
 
-	t.Run("Different", func(t *testing.T) {
-		t.Parallel()
-		hash, err := userpassword.Hash("password")
-		require.NoError(t, err)
-		equal, err := userpassword.Compare(hash, "notpassword")
-		require.NoError(t, err)
-		require.False(t, equal)
-	})
+func TestUserPasswordCompare(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name               string
+		passwordToValidate string
+		password           string
+		shouldHash         bool
+		wantErr            bool
+		wantEqual          bool
+	}{
+		{
+			name:               "Legacy",
+			passwordToValidate: "$pbkdf2-sha256$65535$z8c1p1C2ru9EImBP1I+ZNA$pNjE3Yk0oG0PmJ0Je+y7ENOVlSkn/b0BEqqdKsq6Y97wQBq0xT+lD5bWJpyIKJqQICuPZcEaGDKrXJn8+SIHRg",
+			password:           "tomato",
+			shouldHash:         false,
+			wantErr:            false,
+			wantEqual:          true,
+		},
+		{
+			name:               "Same",
+			passwordToValidate: "password",
+			password:           "password",
+			shouldHash:         true,
+			wantErr:            false,
+			wantEqual:          true,
+		},
+		{
+			name:               "Different",
+			passwordToValidate: "password",
+			password:           "notpassword",
+			shouldHash:         true,
+			wantErr:            false,
+			wantEqual:          false,
+		},
+		{
+			name:               "Invalid",
+			passwordToValidate: "invalidhash",
+			password:           "password",
+			shouldHash:         false,
+			wantErr:            true,
+			wantEqual:          false,
+		},
+		{
+			name:               "InvalidParts",
+			passwordToValidate: "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz",
+			password:           "test",
+			shouldHash:         false,
+			wantErr:            true,
+			wantEqual:          false,
+		},
+	}
 
-	t.Run("Invalid", func(t *testing.T) {
-		t.Parallel()
-		equal, err := userpassword.Compare("invalidhash", "password")
-		require.False(t, equal)
-		require.Error(t, err)
-	})
-
-	t.Run("InvalidParts", func(t *testing.T) {
-		t.Parallel()
-		equal, err := userpassword.Compare("abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz", "test")
-		require.False(t, equal)
-		require.Error(t, err)
-	})
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			if tt.shouldHash {
+				hash, err := userpassword.Hash(tt.passwordToValidate)
+				require.NoError(t, err)
+				tt.passwordToValidate = hash
+			}
+			equal, err := userpassword.Compare(tt.passwordToValidate, tt.password)
+			if tt.wantErr {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+			require.Equal(t, tt.wantEqual, equal)
+		})
+	}
 }