feat(confidentialhttp): AuthConfig for pluggable signing

cre/capabilities/networking/confidentialhttp/v1alpha/client.proto

@@ -60,6 +60,151 @@ message HTTPResponse {
 message ConfidentialHTTPRequest {
   repeated SecretIdentifier vault_don_secrets = 1;
   HTTPRequest request = 2;
+  // auth, when set, instructs the enclave to sign the outbound request using
+  // the specified method. Every secret_name referenced inside AuthConfig must
+  // also appear in vault_don_secrets (enforced by the capability validator).
+  // When auth is nil, the request is sent with only the headers/body the
+  // caller provided — preserving the legacy "{{.SECRET_NAME}}" header-template
+  // behavior.
+  optional AuthConfig auth = 3;
+}
+
+// AuthConfig selects one of the supported request-signing methods.
+// Each variant carries the method-specific parameters and references
+// the names of the Vault-DON secrets it needs.
+message AuthConfig {
+  oneof method {
+    ApiKeyAuth api_key = 1;
+    BasicAuth basic = 2;
+    BearerAuth bearer = 3;
+    HmacAuth hmac = 4;
+    OAuth2Auth oauth2 = 5;
+  }
+}
+
+// ApiKeyAuth attaches a secret value to a chosen header.
+// Renders as:  <header_name>: <value_prefix><secret-value>
+// Example (header_name="x-api-key", secret_name="coingecko", value_prefix=""):
+//   x-api-key: <secret>
+message ApiKeyAuth {
+  string header_name = 1; // required, e.g. "x-api-key", "Authorization"
+  string secret_name = 2; // required; key into ConfidentialHTTPRequest.vault_don_secrets
+  string value_prefix = 3; // optional, e.g. "ApiKey ", "Token "
+}
+
+// BasicAuth renders: Authorization: Basic base64(username ":" password).
+message BasicAuth {
+  string username_secret_name = 1; // required
+  string password_secret_name = 2; // required
+}
+
+// BearerAuth attaches a pre-issued long-lived token.
+// Default behavior: Authorization: Bearer <token>
+// header_name and value_prefix allow rare overrides (e.g. GitHub's
+// "Authorization: token <pat>").
+message BearerAuth {
+  string token_secret_name = 1; // required
+  string header_name = 2; // optional override, default "Authorization"
+  string value_prefix = 3; // optional override, default "Bearer "
+}
+
+// HmacAuth groups all HMAC-family signing variants.
+message HmacAuth {
+  oneof variant {
+    HmacSha256 sha256 = 1;
+    AwsSigV4 aws_sig_v4 = 2;
+    HmacCustom custom = 3;
+  }
+}
+
+// HmacSha256 implements a generic canonical-string HMAC-SHA256 signature.
+// Canonical string: method "\n" url "\n" sha256(body) "\n" timestamp
+// Signature is attached via signature_header, timestamp via timestamp_header.
+message HmacSha256 {
+  string secret_name = 1; // required shared secret
+  string signature_header = 2; // default "X-Signature"
+  string timestamp_header = 3; // default "X-Timestamp"
+  bool include_query = 4; // if true, include the query string in the canonical url
+  string encoding = 5; // "hex" (default) or "base64"
+}
+
+// AwsSigV4 implements AWS Signature Version 4.
+// Uses github.com/aws/aws-sdk-go-v2/aws/signer/v4 under the hood.
+message AwsSigV4 {
+  string access_key_id_secret_name = 1; // required
+  string secret_access_key_secret_name = 2; // required
+  string session_token_secret_name = 3; // optional (for STS creds)
+  string region = 4; // required, e.g. "us-east-1"
+  string service = 5; // required, e.g. "execute-api", "s3"
+  // Signed headers (comma-separated lowercase). Optional; defaults to
+  // "host;x-amz-date" plus "x-amz-security-token" if session_token_secret_name
+  // is set.
+  repeated string signed_headers = 6;
+  // If true, uses X-Amz-Content-Sha256: UNSIGNED-PAYLOAD (useful for large S3
+  // uploads). Default false.
+  bool unsigned_payload = 7;
+}
+
+// HmacCustom lets workflow authors specify the canonical string via a
+// Go text/template string. Available template vars:
+//   {{.method}} {{.url}} {{.path}} {{.query}} {{.body}} {{.body_sha256}}
+//   {{.timestamp}} {{.nonce}} {{header "X-Foo"}}
+message HmacCustom {
+  string secret_name = 1; // required
+  string canonical_template = 2; // required
+  enum Hash {
+    HASH_SHA256 = 0;
+    HASH_SHA512 = 1;
+  }
+  Hash hash = 3;
+  string signature_header = 4; // required
+  string signature_prefix = 5; // e.g. "HMAC-SHA256 "
+  string timestamp_header = 6; // optional; if set, timestamp header injected
+  string nonce_header = 7; // optional; if set, random nonce header injected
+  string encoding = 8; // "hex" (default) or "base64"
+}
+
+// OAuth2Auth groups headless OAuth 2.0 flows.
+// Interactive flows (Authorization Code, PKCE, Device Code) are NOT supported —
+// they require browser consent that a headless TEE cannot perform.
+message OAuth2Auth {
+  oneof variant {
+    OAuth2ClientCredentials client_credentials = 1;
+    OAuth2RefreshToken refresh_token = 2;
+  }
+}
+
+// OAuth2ClientCredentials: machine-to-machine grant.
+// The enclave POSTs to token_url with client_id/client_secret, caches the
+// resulting access_token per (workflow_owner, token_url, client_id, scopes),
+// and attaches "Authorization: Bearer <access_token>" to the outbound request.
+message OAuth2ClientCredentials {
+  string token_url = 1; // required, must be https://
+  string client_id_secret_name = 2; // required
+  string client_secret_secret_name = 3; // required
+  repeated string scopes = 4; // optional
+  string audience = 5; // optional (Auth0-style)
+  // "basic_auth" (default) or "request_body" — where to put client creds
+  // on the token request.
+  string client_auth_method = 6;
+  // Extra form params to send with the token request.
+  map<string, string> extra_params = 7;
+}
+
+// OAuth2RefreshToken: the workflow stores a long-lived refresh_token in Vault
+// (obtained out-of-band during an interactive consent). The enclave exchanges
+// it for an access_token on cache miss.
+//
+// Important: if the IdP rotates refresh tokens on each exchange, the enclave
+// cannot persist the new refresh_token back to Vault. Disable refresh-token
+// rotation at the IdP, or prefer client_credentials where possible.
+message OAuth2RefreshToken {
+  string token_url = 1; // required, must be https://
+  string refresh_token_secret_name = 2; // required
+  string client_id_secret_name = 3; // optional (some IdPs require)
+  string client_secret_secret_name = 4; // optional (some IdPs require)
+  repeated string scopes = 5; // optional
+  map<string, string> extra_params = 6;
 }
 
 service Client {