fix(api): fixed error handeling in authentication middleware

[dvjsharma]

Description

This PR solves the nil pointer dereference issue(internal server error) highlighted in #28

Changes

In the authentication middleware, the err variable is used inconsistently. Please refer to the snippet below-

LicenseDb/pkg/auth/auth.go

Lines 194 to 207 in aa42310

	decodedAuth, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(authHeader, "Basic "))
	if err != nil {
	er := models.LicenseError{
	Status: http.StatusUnauthorized,
	Message: "Please check your credentials and try again",
	Error: err.Error(),
	Path: c.Request.URL.Path,
	Timestamp: time.Now().Format(time.RFC3339),
	}
	c.JSON(http.StatusUnauthorized, er)
	c.Abort()
	return
	}

Here the err variable is appropriately used to capture potential errors during the base64 decoding process, but it is incorrectly used further in the code.

LicenseDb/pkg/auth/auth.go

Lines 219 to 247 in aa42310

	result := db.DB.Where(models.User{Username: username}).First(&user)
	if result.Error != nil {
	er := models.LicenseError{
	Status: http.StatusUnauthorized,
	Message: "User name not found",
	Error: err.Error(),
	Path: c.Request.URL.Path,
	Timestamp: time.Now().Format(time.RFC3339),
	}
	c.JSON(http.StatusUnauthorized, er)
	c.Abort()
	return
	}
	// Check if the password matches
	if *user.Userpassword != password {
	er := models.LicenseError{
	Status: http.StatusUnauthorized,
	Message: "Incorrect password",
	Error: err.Error(),
	Path: c.Request.URL.Path,
	Timestamp: time.Now().Format(time.RFC3339),
	}
	c.JSON(http.StatusUnauthorized, er)
	c.Abort()
	return
	}

At line 224, err.Error() references to decoding errors but it should be referencing to the errors occurring during GORM db querying process happening at line 219. Hence it is replaced by result.Error.Error() to deliever GORM specific errors.

Furthermore, line 239 is also modified to give 'Password does not match' error rather than err.Error().

Fixes #28
CC @GMishx

[GMishx]

Changes looks good.

[GMishx]

Tested, working as expected.