export declare enum CredentialHeader {
    Authorization = "authorization",
    XApiKey = "x-api-key",
    XGoogApiKey = "x-goog-api-key"
}
export type HeaderLookup = (name: string) => string | undefined;
export type CredentialExtractor = (getHeader: HeaderLookup) => string | null;
export declare const credentialExtractor: (header: CredentialHeader) => CredentialExtractor;
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