Any Solution

I can't help you with the certificate stuff, but I can help you with the error:

error: "can't use non-numeric string as operand of "!""

This is caused by the line:

if { not $new_uri starts_with "/" } { 

The "not" operator has higher precendence than the "starts_with" operator. This means that the not is applied to the operand to it's right before the starts_with operator is applied to its operands. Anotherwards, the default result of precendence can be more clearly shown with parenthesis:

if { (not $new_uri) starts_with "/" } { 

Clearly, this is not what you would actually want as taking the not of a string value makes no sense. Unfortunately, this particular order of precedence is specific to Tcl and common to many other programming languages like C, C++, Java, etc.

To solve your problem, simply add some parenthesis like so:

if { not ( $new_uri starts_with "/" ) } { 

Hope this helps.