Invalid length for a Base-64 char array

Solution 1:

The length of a base64 encoded string is always a multiple of 4. If it is not a multiple of 4, then = characters are appended until it is. A query string of the form ?name=value has problems when the value contains = charaters (some of them will be dropped, I don't recall the exact behavior). You may be able to get away with appending the right number of = characters before doing the base64 decode.

Edit 1

You may find that the value of UserNameToVerify has had "+"'s changed to " "'s so you may need to do something like so:

a = a.Replace(" ", "+");

This should get the length right;

int mod4 = a.Length % 4;
if (mod4 > 0 )
{
    a += new string('=', 4 - mod4);
}

Of course calling UrlEncode (as in LukeH's answer) should make this all moot.

Solution 2:

My guess is that you simply need to URL-encode your Base64 string when you include it in the querystring.

Base64 encoding uses some characters which must be encoded if they're part of a querystring (namely + and /, and maybe = too). If the string isn't correctly encoded then you won't be able to decode it successfully at the other end, hence the errors.

You can use the HttpUtility.UrlEncode method to encode your Base64 string:

string msg = "Please click on the link below or paste it into a browser "
             + "to verify your email account.<br /><br /><a href=\""
             + _configuration.RootURL + "Accounts/VerifyEmail.aspx?a="
             + HttpUtility.UrlEncode(userName.Encrypt("verify")) + "\">"
             + _configuration.RootURL + "Accounts/VerifyEmail.aspx?a="
             + HttpUtility.UrlEncode(userName.Encrypt("verify")) + "</a>";