Function computeDigestResponse

computeDigestResponse(
    challenge: DigestChallenge,
    username: string,
    password: string,
    method: string,
    uri: string,
    cnonce?: string,
    nc?: string,
): Promise<string>
Compute the Digest Access Authentication response value per RFC 7616 §3.4.

The response is computed as:
```
HA1  = H(username:realm:password)
HA2  = H(method:uri)
response = H(HA1:nonce[:nc:cnonce:qop]:HA2)    // when qop is present
response = H(HA1:nonce:HA2)                     // when qop is absent
```
where H is the hash algorithm selected by the challenge (MD5, SHA-256, or SHA-512-256). Defaults to MD5 per RFC 7616 §3.4.1.
Parameters
- challenge: DigestChallenge
  Parsed challenge from the server's WWW-Authenticate header.
- username: string
  Digest auth username.
- password: string
  Digest auth password.
- method: string
  HTTP method (e.g. "GET", "POST").
- uri: string
  Request URI path + query (e.g. "/dir/index.html").
- Optionalcnonce: string
  Client nonce (random). Auto-generated if omitted.
- Optionalnc: string
  Nonce count as 8-char zero-padded hex (e.g. "00000001"). Defaults to "00000001" if omitted.
Returns Promise<string>
The hex-encoded response hash.
Example
```
const challenge = parseDigestChallenge(wwwAuthHeader);
const response = await computeDigestResponse(challenge, "Mufasa",
  "Circle Of Life", "GET", "/dir/index.html");
```
- Defined in src/digest.ts:495